diff --git a/lib/6to5/to-fast-properties.js b/lib/6to5/to-fast-properties.js
new file mode 100644
index 0000000000..341a451d03
--- /dev/null
+++ b/lib/6to5/to-fast-properties.js
@@ -0,0 +1,14 @@
+/**
+ * A trick from Bluebird to force V8 to use fast properties for an object.
+ * Read more: http://stackoverflow.com/questions/24987896/
+ *
+ * Use %HasFastProperties(obj) and --allow-natives-syntax to check whether
+ * a particular object already has fast properties.
+ */
+module.exports = function toFastProperties(obj) {
+  /*jshint -W027*/
+  function f() {}
+  f.prototype = obj;
+  return f;
+  eval(obj);
+};
diff --git a/lib/6to5/transformation/helpers/name-method.js b/lib/6to5/transformation/helpers/name-method.js
index 00d3c77a08..36cdbddaea 100644
--- a/lib/6to5/transformation/helpers/name-method.js
+++ b/lib/6to5/transformation/helpers/name-method.js
@@ -2,6 +2,24 @@ var traverse = require("../../traverse");
 var util     = require("../../util");
 var t        = require("../../types");
 
+var traverser = {
+  enter: function (node, parent, scope, context, state) {
+    // check if this node is an identifier that matches the same as our function id
+    if (!t.isIdentifier(node, { name: state.id })) return;
+
+    // check if this node is the one referenced
+    if (!t.isReferenced(node, parent)) return;
+
+    // check that we don't have a local variable declared as that removes the need
+    // for the wrapper
+    var localDeclar = scope.get(state.id, true);
+    if (localDeclar !== state.outerDeclar) return;
+
+    state.selfReference = true;
+    context.stop();
+  }
+};
+
 module.exports = function (node, file, scope) {
   var key = t.toComputedKey(node, node.key);
   if (!t.isLiteral(key)) return node; // we can't set a function id with this
@@ -9,28 +27,15 @@ module.exports = function (node, file, scope) {
   var id = t.toIdentifier(key.value);
   key = t.identifier(id);
 
-  var selfReference = false;
-  var outerDeclar = scope.get(id, true);
+  var state = {
+    id: id,
+    selfReference: false,
+    outerDeclar: scope.get(id, true),
+  };
 
-  traverse(node, {
-    enter: function (node, parent, scope) {
-      // check if this node is an identifier that matches the same as our function id
-      if (!t.isIdentifier(node, { name: id })) return;
+  traverse(node, traverser, scope, state);
 
-      // check if this node is the one referenced
-      if (!t.isReferenced(node, parent)) return;
-
-      // check that we don't have a local variable declared as that removes the need
-      // for the wrapper
-      var localDeclar = scope.get(id, true);
-      if (localDeclar !== outerDeclar) return;
-
-      selfReference = true;
-      this.stop();
-    }
-  }, scope);
-
-  if (selfReference) {
+  if (state.selfReference) {
     node.value = util.template("property-method-assignment-wrapper", {
       FUNCTION: node.value,
       FUNCTION_ID: key,
diff --git a/lib/6to5/transformation/helpers/remap-async-to-generator.js b/lib/6to5/transformation/helpers/remap-async-to-generator.js
index 86a2c00ba7..7868e86ec7 100644
--- a/lib/6to5/transformation/helpers/remap-async-to-generator.js
+++ b/lib/6to5/transformation/helpers/remap-async-to-generator.js
@@ -6,8 +6,8 @@ module.exports = function (node, callId) {
   node.generator = true;
 
   traverse(node, {
-    enter: function (node) {
-      if (t.isFunction(node)) this.skip();
+    enter: function (node, parent, scope, context) {
+      if (t.isFunction(node)) context.skip();
 
       if (t.isAwaitExpression(node)) {
         node.type = "YieldExpression";
diff --git a/lib/6to5/transformation/modules/_default.js b/lib/6to5/transformation/modules/_default.js
index 42e377b3a8..1485d27f03 100644
--- a/lib/6to5/transformation/modules/_default.js
+++ b/lib/6to5/transformation/modules/_default.js
@@ -16,35 +16,51 @@ function DefaultFormatter(file) {
   //this.checkCollisions();
 }
 
+var exportsTraverser = {
+  enter: function (node, parent, scope, context, localExports) {
+    var declar = node && node.declaration;
+    if (t.isExportDeclaration(node) && declar && t.isStatement(declar)) {
+      _.extend(localExports, t.getIds(declar, true));
+    }
+  }
+};
+
 DefaultFormatter.prototype.getLocalExports = function () {
   var localExports = {};
-
-  traverse(this.file.ast, {
-    enter: function (node) {
-      var declar = node && node.declaration;
-      if (t.isExportDeclaration(node) && declar && t.isStatement(declar)) {
-        _.extend(localExports, t.getIds(declar, true));
-      }
-    }
-  });
-
+  traverse(this.file.ast, exportsTraverser, null, localExports);
   return localExports;
 };
 
+var importsTraverser = {
+  enter: function (node, parent, scope, context, localImports) {
+    if (t.isImportDeclaration(node)) {
+      _.extend(localImports, t.getIds(node, true));
+    }
+  }
+};
+
 DefaultFormatter.prototype.getLocalImports = function () {
   var localImports = {};
-
-  traverse(this.file.ast, {
-    enter: function (node) {
-      if (t.isImportDeclaration(node)) {
-        _.extend(localImports, t.getIds(node, true));
-      }
-    }
-  });
-
+  traverse(this.file.ast, importsTraverser, null, localImports);
   return localImports;
 };
 
+var collissionsTraverser = {
+  enter: function (node, parent, scope, context, check) {
+    if (t.isAssignmentExpression(node)) {
+
+      var left = node.left;
+      if (t.isMemberExpression(left)) {
+        while (left.object) left = left.object;
+      }
+
+      check(left);
+    } else if (t.isDeclaration(node)) {
+      _.each(t.getIds(node, true), check);
+    }
+  }
+};
+
 DefaultFormatter.prototype.checkCollisions = function () {
   // todo: all check export collissions
 
@@ -61,21 +77,7 @@ DefaultFormatter.prototype.checkCollisions = function () {
     }
   };
 
-  traverse(file.ast, {
-    enter: function (node) {
-      if (t.isAssignmentExpression(node)) {
-
-        var left = node.left;
-        if (t.isMemberExpression(left)) {
-          while (left.object) left = left.object;
-        }
-
-        check(left);
-      } else if (t.isDeclaration(node)) {
-        _.each(t.getIds(node, true), check);
-      }
-    }
-  });
+  traverse(file.ast, collissionsTraverser, null, check);
 };
 
 DefaultFormatter.prototype.remapExportAssignment = function (node) {
@@ -100,9 +102,9 @@ DefaultFormatter.prototype.remapAssignments = function () {
   };
 
   traverse(this.file.ast, {
-    enter: function (node, parent, scope) {
+    enter: function (node, parent, scope, context, isLocalReference) {
       if (t.isUpdateExpression(node) && isLocalReference(node.argument, scope)) {
-        this.skip();
+        context.skip();
 
         // expand to long file assignment expression
         var assign = t.assignmentExpression(node.operator[0] + "=", node.argument, t.literal(1));
@@ -130,11 +132,11 @@ DefaultFormatter.prototype.remapAssignments = function () {
       }
 
       if (t.isAssignmentExpression(node) && isLocalReference(node.left, scope)) {
-        this.skip();
+        context.skip();
         return self.remapExportAssignment(node);
       }
     }
-  });
+  }, null, isLocalReference);
 };
 
 DefaultFormatter.prototype.getModuleName = function () {
diff --git a/lib/6to5/transformation/modules/system.js b/lib/6to5/transformation/modules/system.js
index b70c8423a4..d0650a69c2 100644
--- a/lib/6to5/transformation/modules/system.js
+++ b/lib/6to5/transformation/modules/system.js
@@ -63,28 +63,31 @@ SystemFormatter.prototype.importSpecifier = function (specifier, node, nodes) {
 
 SystemFormatter.prototype.buildRunnerSetters = function (block, hoistDeclarators) {
   return t.arrayExpression(_.map(this.ids, function (uid, source) {
-    var nodes = [];
+    var state = {
+      nodes: [],
+      hoistDeclarators: hoistDeclarators
+    };
 
     traverse(block, {
-      enter: function (node) {
+      enter: function (node, parent, scope, context, state) {
         if (node._importSource === source) {
           if (t.isVariableDeclaration(node)) {
             _.each(node.declarations, function (declar) {
-              hoistDeclarators.push(t.variableDeclarator(declar.id));
-              nodes.push(t.expressionStatement(
+              state.hoistDeclarators.push(t.variableDeclarator(declar.id));
+              state.nodes.push(t.expressionStatement(
                 t.assignmentExpression("=", declar.id, declar.init)
               ));
             });
           } else {
-            nodes.push(node);
+            state.nodes.push(node);
           }
 
-          this.remove();
+          context.remove();
         }
       }
-    });
+    }, null, state);
 
-    return t.functionExpression(null, [uid], t.blockStatement(nodes));
+    return t.functionExpression(null, [uid], t.blockStatement(state.nodes));
   }));
 };
 
@@ -112,10 +115,10 @@ SystemFormatter.prototype.transform = function (ast) {
 
   // hoist up all variable declarations
   traverse(block, {
-    enter: function (node, parent, scope) {
+    enter: function (node, parent, scope, context, hoistDeclarators) {
       if (t.isFunction(node)) {
         // nothing inside is accessible
-        return this.skip();
+        return context.skip();
       }
 
       if (t.isVariableDeclaration(node)) {
@@ -150,7 +153,8 @@ SystemFormatter.prototype.transform = function (ast) {
         return nodes;
       }
     }
-  });
+  }, null, hoistDeclarators);
+
   if (hoistDeclarators.length) {
     var hoistDeclar = t.variableDeclaration("var", hoistDeclarators);
     hoistDeclar._blockHoist = true;
@@ -159,15 +163,15 @@ SystemFormatter.prototype.transform = function (ast) {
 
   // hoist up function declarations for circular references
   traverse(block, {
-    enter: function (node) {
-      if (t.isFunction(node)) this.skip();
+    enter: function (node, parent, scope, context, handlerBody) {
+      if (t.isFunction(node)) context.skip();
 
       if (t.isFunctionDeclaration(node) || node._blockHoist) {
         handlerBody.push(node);
-        this.remove();
+        context.remove();
       }
     }
-  });
+  }, null, handlerBody);
 
   handlerBody.push(returnStatement);
 
diff --git a/lib/6to5/transformation/transformer.js b/lib/6to5/transformation/transformer.js
index f4de701b51..dbcd0f9d10 100644
--- a/lib/6to5/transformation/transformer.js
+++ b/lib/6to5/transformation/transformer.js
@@ -4,6 +4,25 @@ var traverse = require("../traverse");
 var t        = require("../types");
 var _        = require("lodash");
 
+function noop() { }
+
+function enter(node, parent, scope, context, args) {
+  var fns = args[1][node.type];
+  if (!fns) return;
+  return fns.enter(node, parent, scope, context, args[0]);
+}
+
+function exit(node, parent, scope, context, args) {
+  var fns = args[1][node.type];
+  if (!fns) return;
+  return fns.exit(node, parent, scope, context, args[0]);
+}
+
+var traverseOpts = {
+  enter: enter,
+  exit: exit
+};
+
 function Transformer(key, transformer, opts) {
   this.manipulateOptions = transformer.manipulateOptions;
   this.experimental      = !!transformer.experimental;
@@ -32,6 +51,9 @@ Transformer.prototype.normalise = function (transformer) {
 
     if (!_.isObject(fns)) return;
 
+    if (!fns.enter) fns.enter = noop;
+    if (!fns.exit) fns.exit = noop;
+
     transformer[type] = fns;
 
     var aliases = t.FLIPPED_ALIAS_KEYS[type];
@@ -54,28 +76,8 @@ Transformer.prototype.astRun = function (file, key) {
 };
 
 Transformer.prototype.transform = function (file) {
-  var transformer = this.transformer;
-
-  var build = function (exit) {
-    return function (node, parent, scope) {
-      var fns = transformer[node.type];
-      if (!fns) return;
-
-      var fn = fns.enter;
-      if (exit) fn = fns.exit;
-      if (!fn) return;
-
-      return fn.call(this, node, parent, file, scope);
-    };
-  };
-
   this.astRun(file, "before");
-
-  traverse(file.ast, {
-    enter: build(),
-    exit:  build(true)
-  });
-
+  traverse(file.ast, traverseOpts, null, [file, this.transformer]);
   this.astRun(file, "after");
 };
 
diff --git a/lib/6to5/transformation/transformers/_alias-functions.js b/lib/6to5/transformation/transformers/_alias-functions.js
index 5cf9003c84..1d2bf585f6 100644
--- a/lib/6to5/transformation/transformers/_alias-functions.js
+++ b/lib/6to5/transformation/transformers/_alias-functions.js
@@ -1,57 +1,62 @@
 var traverse = require("../../traverse");
 var t        = require("../../types");
 
+var functionChildrenTraverser = {
+  enter: function (node, parent, scope, context, state) {
+    if (t.isFunction(node) && !node._aliasFunction) {
+      return context.skip();
+    }
+
+    if (node._ignoreAliasFunctions) return context.skip();
+
+    var getId;
+
+    if (t.isIdentifier(node) && node.name === "arguments") {
+      getId = state.getArgumentsId;
+    } else if (t.isThisExpression(node)) {
+      getId = state.getThisId;
+    } else {
+      return;
+    }
+
+    if (t.isReferenced(node, parent)) return getId();
+  }
+};
+
+var functionTraverser = {
+  enter: function (node, parent, scope, context, state) {
+    if (!node._aliasFunction) {
+      if (t.isFunction(node)) {
+        // stop traversal of this node as it'll be hit again by this transformer
+        return context.skip();
+      } else {
+        return;
+      }
+    }
+
+    // traverse all child nodes of this function and find `arguments` and `this`
+    traverse(node, functionChildrenTraverser, null, state);
+
+    return context.skip();
+  }
+};
+
 var go = function (getBody, node, file, scope) {
   var argumentsId;
   var thisId;
 
-  var getArgumentsId = function () {
-    return argumentsId = argumentsId || file.generateUidIdentifier("arguments", scope);
-  };
-
-  var getThisId = function () {
-    return thisId = thisId || file.generateUidIdentifier("this", scope);
+  var state = {
+    getArgumentsId: function () {
+      return argumentsId = argumentsId || file.generateUidIdentifier("arguments", scope);
+    },
+    getThisId: function () {
+      return thisId = thisId || file.generateUidIdentifier("this", scope);
+    }
   };
 
   // traverse the function and find all alias functions so we can alias
   // `arguments` and `this` if necessary
-  traverse(node, {
-    enter: function (node) {
-      if (!node._aliasFunction) {
-        if (t.isFunction(node)) {
-          // stop traversal of this node as it'll be hit again by this transformer
-          return this.skip();
-        } else {
-          return;
-        }
-      }
-
-      // traverse all child nodes of this function and find `arguments` and `this`
-      traverse(node, {
-        enter: function (node, parent) {
-          if (t.isFunction(node) && !node._aliasFunction) {
-            return this.skip();
-          }
-
-          if (node._ignoreAliasFunctions) return this.skip();
-
-          var getId;
-
-          if (t.isIdentifier(node) && node.name === "arguments") {
-            getId = getArgumentsId;
-          } else if (t.isThisExpression(node)) {
-            getId = getThisId;
-          } else {
-            return;
-          }
-
-          if (t.isReferenced(node, parent)) return getId();
-        }
-      });
-
-      return this.skip();
-    }
-  });
+  traverse(node, functionTraverser, null, state);
 
   var body;
 
@@ -71,14 +76,14 @@ var go = function (getBody, node, file, scope) {
   }
 };
 
-exports.Program = function (node, parent, file, scope) {
+exports.Program = function (node, parent, scope, context, file) {
   go(function () {
     return node.body;
   }, node, file, scope);
 };
 
 exports.FunctionDeclaration =
-exports.FunctionExpression = function (node, parent, file, scope) {
+exports.FunctionExpression = function (node, parent, scope, context, file) {
   go(function () {
     t.ensureBlock(node);
     return node.body.body;
diff --git a/lib/6to5/transformation/transformers/es6-classes.js b/lib/6to5/transformation/transformers/es6-classes.js
index dc079ca164..18f24c4031 100644
--- a/lib/6to5/transformation/transformers/es6-classes.js
+++ b/lib/6to5/transformation/transformers/es6-classes.js
@@ -3,11 +3,11 @@ var traverse   = require("../../traverse");
 var util       = require("../../util");
 var t          = require("../../types");
 
-exports.ClassDeclaration = function (node, parent, file, scope) {
+exports.ClassDeclaration = function (node, parent, scope, context, file) {
   return new Class(node, file, scope, true).run();
 };
 
-exports.ClassExpression = function (node, parent, file, scope) {
+exports.ClassExpression = function (node, parent, scope, context, file) {
   if (!node.id) {
     if (t.isProperty(parent) && parent.value === node && !parent.computed && t.isIdentifier(parent.key)) {
       // var o = { foo: class {} };
@@ -316,16 +316,16 @@ Class.prototype.replaceSuperReferences = function (methodNode) {
 
   function traverseLevel(node, topLevel) {
     traverse(node, {
-      enter: function (node, parent) {
+      enter: function (node, parent, scope, context) {
         if (t.isFunction(node) && !t.isArrowFunctionExpression(node)) {
           // we need to call traverseLevel again so we're context aware
           traverseLevel(node, false);
-          return this.skip();
+          return context.skip();
         }
 
         if (t.isProperty(node, { method: true }) || t.isMethodDefinition(node)) {
           // break on object methods
-          return this.skip();
+          return context.skip();
         }
 
         var getThisReference = function () {
diff --git a/lib/6to5/transformation/transformers/es6-computed-property-names.js b/lib/6to5/transformation/transformers/es6-computed-property-names.js
index dcfff3b827..3789ca1d23 100644
--- a/lib/6to5/transformation/transformers/es6-computed-property-names.js
+++ b/lib/6to5/transformation/transformers/es6-computed-property-names.js
@@ -1,6 +1,6 @@
 var t = require("../../types");
 
-exports.ObjectExpression = function (node, parent, file, scope) {
+exports.ObjectExpression = function (node, parent, scope, context, file) {
   var hasComputed = false;
 
   for (var i = 0; i < node.properties.length; i++) {
diff --git a/lib/6to5/transformation/transformers/es6-constants.js b/lib/6to5/transformation/transformers/es6-constants.js
index dc8e0ce49e..096eee9097 100644
--- a/lib/6to5/transformation/transformers/es6-constants.js
+++ b/lib/6to5/transformation/transformers/es6-constants.js
@@ -6,7 +6,7 @@ exports.Program =
 exports.BlockStatement =
 exports.ForInStatement =
 exports.ForOfStatement =
-exports.ForStatement = function (node, parent, file) {
+exports.ForStatement = function (node, parent, scope, context, file) {
   var hasConstants = false;
   var constants = {};
 
@@ -69,14 +69,19 @@ exports.ForStatement = function (node, parent, file) {
 
   if (!hasConstants) return;
 
+  var state = {
+    check: check,
+    getIds: getIds
+  };
+
   traverse(node, {
-    enter: function (child, parent, scope) {
+    enter: function (child, parent, scope, context, state) {
       if (child._ignoreConstant) return;
       if (t.isVariableDeclaration(child)) return;
 
       if (t.isVariableDeclarator(child) || t.isDeclaration(child) || t.isAssignmentExpression(child)) {
-        check(parent, getIds(child), scope);
+        state.check(parent, state.getIds(child), scope);
       }
     }
-  });
+  }, null, state);
 };
diff --git a/lib/6to5/transformation/transformers/es6-default-parameters.js b/lib/6to5/transformation/transformers/es6-default-parameters.js
index 0d99b6db8e..4b03d56295 100644
--- a/lib/6to5/transformation/transformers/es6-default-parameters.js
+++ b/lib/6to5/transformation/transformers/es6-default-parameters.js
@@ -2,7 +2,7 @@ var traverse = require("../../traverse");
 var util     = require("../../util");
 var t        = require("../../types");
 
-exports.Function = function (node, parent, file, scope) {
+exports.Function = function (node, parent, scope, context, file) {
   if (!node.defaults || !node.defaults.length) return;
   t.ensureBlock(node);
 
diff --git a/lib/6to5/transformation/transformers/es6-destructuring.js b/lib/6to5/transformation/transformers/es6-destructuring.js
index 22d016b38f..bcd04ba4b2 100644
--- a/lib/6to5/transformation/transformers/es6-destructuring.js
+++ b/lib/6to5/transformation/transformers/es6-destructuring.js
@@ -148,7 +148,7 @@ var pushPattern = function (opts) {
 };
 
 exports.ForInStatement =
-exports.ForOfStatement = function (node, parent, file, scope) {
+exports.ForOfStatement = function (node, parent, scope, context, file) {
   var declar = node.left;
   if (!t.isVariableDeclaration(declar)) return;
 
@@ -174,7 +174,7 @@ exports.ForOfStatement = function (node, parent, file, scope) {
   block.body = nodes.concat(block.body);
 };
 
-exports.Function = function (node, parent, file, scope) {
+exports.Function = function (node, parent, scope, context, file) {
   var nodes = [];
 
   var hasDestructuring = false;
@@ -205,7 +205,7 @@ exports.Function = function (node, parent, file, scope) {
   block.body = nodes.concat(block.body);
 };
 
-exports.CatchClause = function (node, parent, file, scope) {
+exports.CatchClause = function (node, parent, scope, context, file) {
   var pattern = node.param;
   if (!t.isPattern(pattern)) return;
 
@@ -223,7 +223,7 @@ exports.CatchClause = function (node, parent, file, scope) {
   node.body.body = nodes.concat(node.body.body);
 };
 
-exports.ExpressionStatement = function (node, parent, file, scope) {
+exports.ExpressionStatement = function (node, parent, scope, context, file) {
   var expr = node.expression;
   if (expr.type !== "AssignmentExpression") return;
 
@@ -245,7 +245,7 @@ exports.ExpressionStatement = function (node, parent, file, scope) {
   return nodes;
 };
 
-exports.AssignmentExpression = function (node, parent, file, scope) {
+exports.AssignmentExpression = function (node, parent, scope, context, file) {
   if (parent.type === "ExpressionStatement") return;
   if (!t.isPattern(node.left)) return;
 
@@ -270,7 +270,7 @@ exports.AssignmentExpression = function (node, parent, file, scope) {
   return t.toSequenceExpression(nodes, scope);
 };
 
-exports.VariableDeclaration = function (node, parent, file, scope) {
+exports.VariableDeclaration = function (node, parent, scope, context, file) {
   if (t.isForInStatement(parent) || t.isForOfStatement(parent)) return;
 
   var nodes = [];
diff --git a/lib/6to5/transformation/transformers/es6-for-of.js b/lib/6to5/transformation/transformers/es6-for-of.js
index 61357cfbad..9018e995af 100644
--- a/lib/6to5/transformation/transformers/es6-for-of.js
+++ b/lib/6to5/transformation/transformers/es6-for-of.js
@@ -1,11 +1,11 @@
 var util = require("../../util");
 var t    = require("../../types");
 
-exports.ForOfStatement = function (node, parent, file, scope) {
+exports.ForOfStatement = function (node, parent, scope, context, file) {
   var callback = spec;
   if (file.isLoose("forOf")) callback = loose;
 
-  var build  = callback(node, parent, file, scope);
+  var build  = callback(node, parent, scope, context, file);
   var declar = build.declar;
   var loop   = build.loop;
   var block  = loop.body;
@@ -31,7 +31,7 @@ exports.ForOfStatement = function (node, parent, file, scope) {
   return loop;
 };
 
-var loose = function (node, parent, file, scope) {
+var loose = function (node, parent, scope, context, file) {
   var left = node.left;
   var declar, id;
 
@@ -63,7 +63,7 @@ var loose = function (node, parent, file, scope) {
   };
 };
 
-var spec = function (node, parent, file, scope) {
+var spec = function (node, parent, scope, context, file) {
   var left = node.left;
   var declar;
 
diff --git a/lib/6to5/transformation/transformers/es6-let-scoping.js b/lib/6to5/transformation/transformers/es6-let-scoping.js
index bdce7be036..7c589851cd 100644
--- a/lib/6to5/transformation/transformers/es6-let-scoping.js
+++ b/lib/6to5/transformation/transformers/es6-let-scoping.js
@@ -34,7 +34,7 @@ exports.VariableDeclaration = function (node, parent) {
   isLet(node, parent);
 };
 
-exports.Loop = function (node, parent, file, scope) {
+exports.Loop = function (node, parent, scope, context, file) {
   var init = node.left || node.init;
   if (isLet(init, node)) {
     t.ensureBlock(node);
@@ -46,7 +46,7 @@ exports.Loop = function (node, parent, file, scope) {
     node.label = parent.label;
   }
 
-  var letScoping = new LetScoping(node, node.body, parent, file, scope);
+  var letScoping = new LetScoping(node, node.body, parent, scope, file);
   letScoping.run();
 
   if (node.label && !t.isLabeledStatement(parent)) {
@@ -55,9 +55,9 @@ exports.Loop = function (node, parent, file, scope) {
   }
 };
 
-exports.BlockStatement = function (block, parent, file, scope) {
+exports.BlockStatement = function (block, parent, scope, context, file) {
   if (!t.isLoop(parent)) {
-    var letScoping = new LetScoping(false, block, parent, file, scope);
+    var letScoping = new LetScoping(false, block, parent, scope, file);
     letScoping.run();
   }
 };
@@ -68,11 +68,11 @@ exports.BlockStatement = function (block, parent, file, scope) {
  * @param {Boolean|Node} loopParent
  * @param {Node} block
  * @param {Node} parent
- * @param {File} file
  * @param {Scope} scope
+ * @param {File} file
  */
 
-function LetScoping(loopParent, block, parent, file, scope) {
+function LetScoping(loopParent, block, parent, scope, file) {
   this.loopParent = loopParent;
   this.parent     = parent;
   this.scope      = scope;
@@ -167,7 +167,7 @@ LetScoping.prototype.remap = function () {
 
   if (!this.info.hasDuplicates) return;
 
-  var replace = function (node, parent, scope) {
+  var replace = function (node, parent, scope, context, replacements) {
     if (!t.isIdentifier(node)) return;
     if (!t.isReferenced(node, parent)) return;
     if (scope && scope.hasOwn(node.name)) return;
@@ -176,7 +176,7 @@ LetScoping.prototype.remap = function () {
 
   var traverseReplace = function (node, parent) {
     replace(node, parent);
-    traverse(node, { enter: replace });
+    traverse(node, { enter: replace }, null, replacements);
   };
 
   var loopParent = this.loopParent;
@@ -186,7 +186,7 @@ LetScoping.prototype.remap = function () {
     traverseReplace(loopParent.update, loopParent);
   }
 
-  traverse(block, { enter: replace });
+  traverse(block, { enter: replace }, null, replacements);
 };
 
 /**
@@ -277,11 +277,11 @@ LetScoping.prototype.checkLoop = function () {
   };
 
   traverse(this.block, {
-    enter: function (node, parent) {
+    enter: function (node, parent, scope, context) {
       var replace;
 
       if (t.isFunction(node) || t.isLoop(node)) {
-        return this.skip();
+        return context.skip();
       }
 
       if (node && !node.label) {
@@ -305,7 +305,7 @@ LetScoping.prototype.checkLoop = function () {
 
       if (replace) return t.inherits(replace, node);
     }
-  });
+  }, null, has);
 
   return has;
 };
@@ -316,9 +316,8 @@ LetScoping.prototype.checkLoop = function () {
  */
 
 LetScoping.prototype.hoistVarDeclarations = function () {
-  var self = this;
   traverse(this.block, {
-    enter: function (node, parent) {
+    enter: function (node, parent, scope, context, self) {
       if (t.isForStatement(node)) {
         if (isVar(node.init, node)) {
           node.init = t.sequenceExpression(self.pushDeclar(node.init));
@@ -330,10 +329,10 @@ LetScoping.prototype.hoistVarDeclarations = function () {
       } else if (isVar(node, parent)) {
         return self.pushDeclar(node).map(t.expressionStatement);
       } else if (t.isFunction(node)) {
-        return this.skip();
+        return context.skip();
       }
     }
-  });
+  }, null, this);
 };
 
 /**
@@ -359,13 +358,15 @@ LetScoping.prototype.getParams = function (params) {
  */
 
 LetScoping.prototype.getLetReferences = function () {
-  var closurify = false;
-  var self = this;
+  var state = {
+    self: this,
+    closurify: false
+  };
 
   // traverse through this block, stopping on functions and checking if they
   // contain any outside let references
   traverse(this.block, {
-    enter: function (node, parent, scope) {
+    enter: function (node, parent, scope, context, state) {
       if (t.isFunction(node)) {
         traverse(node, {
           enter: function (node, parent) {
@@ -379,22 +380,22 @@ LetScoping.prototype.getLetReferences = function () {
             // to our let scope
             if (scope.hasOwn(node.name, true)) return;
 
-            closurify = true;
+            state.closurify = true;
 
             // this key doesn't appear just outside our scope
-            if (!_.contains(self.info.outsideKeys, node.name)) return;
+            if (!_.contains(state.self.info.outsideKeys, node.name)) return;
 
             // push this badboy
-            self.letReferences[node.name] = node;
+            state.self.letReferences[node.name] = node;
           }
-        });
+        }, null, state);
 
-        return this.skip();
+        return context.skip();
       }
     }
-  });
+  }, null, state);
 
-  return closurify;
+  return state.closurify;
 };
 
 /**
diff --git a/lib/6to5/transformation/transformers/es6-modules.js b/lib/6to5/transformation/transformers/es6-modules.js
index 9d9631095b..a9b60473f2 100644
--- a/lib/6to5/transformation/transformers/es6-modules.js
+++ b/lib/6to5/transformation/transformers/es6-modules.js
@@ -6,7 +6,7 @@ exports.ast = {
   }
 };
 
-exports.ImportDeclaration = function (node, parent, file) {
+exports.ImportDeclaration = function (node, parent, scope, context, file) {
   var nodes = [];
 
   if (node.specifiers.length) {
@@ -26,7 +26,7 @@ exports.ImportDeclaration = function (node, parent, file) {
   return nodes;
 };
 
-exports.ExportDeclaration = function (node, parent, file) {
+exports.ExportDeclaration = function (node, parent, scope, context, file) {
   var nodes = [];
 
   if (node.declaration) {
diff --git a/lib/6to5/transformation/transformers/es6-property-method-assignment.js b/lib/6to5/transformation/transformers/es6-property-method-assignment.js
index 30a54102a5..7237ef1c4f 100644
--- a/lib/6to5/transformation/transformers/es6-property-method-assignment.js
+++ b/lib/6to5/transformation/transformers/es6-property-method-assignment.js
@@ -2,7 +2,7 @@ var nameMethod = require("../helpers/name-method");
 var util       = require("../../util");
 var t          = require("../../types");
 
-exports.Property = function (node, parent, file, scope) {
+exports.Property = function (node, parent, scope, context, file) {
   if (!node.method) return;
 
   node.method = false;
diff --git a/lib/6to5/transformation/transformers/es6-rest-parameters.js b/lib/6to5/transformation/transformers/es6-rest-parameters.js
index d0757690b4..c618394c51 100644
--- a/lib/6to5/transformation/transformers/es6-rest-parameters.js
+++ b/lib/6to5/transformation/transformers/es6-rest-parameters.js
@@ -1,11 +1,11 @@
 var util = require("../../util");
 var t    = require("../../types");
 
-exports.Function = function (node, parent, file) {
+exports.Function = function (node, parent, scope, context, file) {
   if (!node.rest) return;
 
   var rest = node.rest;
-  delete node.rest;
+  node.rest = null;
 
   t.ensureBlock(node);
 
diff --git a/lib/6to5/transformation/transformers/es6-spread.js b/lib/6to5/transformation/transformers/es6-spread.js
index 8547bfa550..4fa64b5e2b 100644
--- a/lib/6to5/transformation/transformers/es6-spread.js
+++ b/lib/6to5/transformation/transformers/es6-spread.js
@@ -40,7 +40,7 @@ var build = function (props, file) {
   return nodes;
 };
 
-exports.ArrayExpression = function (node, parent, file) {
+exports.ArrayExpression = function (node, parent, scope, context, file) {
   var elements = node.elements;
   if (!hasSpread(elements)) return;
 
@@ -55,7 +55,7 @@ exports.ArrayExpression = function (node, parent, file) {
   return t.callExpression(t.memberExpression(first, t.identifier("concat")), nodes);
 };
 
-exports.CallExpression = function (node, parent, file, scope) {
+exports.CallExpression = function (node, parent, scope, context, file) {
   var args = node.arguments;
   if (!hasSpread(args)) return;
 
@@ -95,7 +95,7 @@ exports.CallExpression = function (node, parent, file, scope) {
   node.arguments.unshift(contextLiteral);
 };
 
-exports.NewExpression = function (node, parent, file) {
+exports.NewExpression = function (node, parent, scope, context, file) {
   var args = node.arguments;
   if (!hasSpread(args)) return;
 
diff --git a/lib/6to5/transformation/transformers/es6-template-literals.js b/lib/6to5/transformation/transformers/es6-template-literals.js
index 8ad54914f7..d2f360b104 100644
--- a/lib/6to5/transformation/transformers/es6-template-literals.js
+++ b/lib/6to5/transformation/transformers/es6-template-literals.js
@@ -4,7 +4,7 @@ var buildBinaryExpression = function (left, right) {
   return t.binaryExpression("+", left, right);
 };
 
-exports.TaggedTemplateExpression = function (node, parent, file) {
+exports.TaggedTemplateExpression = function (node, parent, scope, context, file) {
   var args = [];
   var quasi = node.quasi;
 
diff --git a/lib/6to5/transformation/transformers/es7-abstract-references.js b/lib/6to5/transformation/transformers/es7-abstract-references.js
index 89bc7c05e4..39003b914c 100644
--- a/lib/6to5/transformation/transformers/es7-abstract-references.js
+++ b/lib/6to5/transformation/transformers/es7-abstract-references.js
@@ -21,7 +21,7 @@ var container = function (parent, call, ret) {
   }
 };
 
-exports.AssignmentExpression = function (node, parent, file, scope) {
+exports.AssignmentExpression = function (node, parent, scope, context, file) {
   var left = node.left;
   if (!t.isVirtualPropertyExpression(left)) return;
 
@@ -74,7 +74,7 @@ exports.UnaryExpression = function (node, parent) {
   return container(parent, call, t.literal(true));
 };
 
-exports.CallExpression = function (node, parent, file, scope) {
+exports.CallExpression = function (node, parent, scope, context, file) {
   var callee = node.callee;
   if (!t.isVirtualPropertyExpression(callee)) return;
 
diff --git a/lib/6to5/transformation/transformers/es7-array-comprehension.js b/lib/6to5/transformation/transformers/es7-array-comprehension.js
index 0a18a94e8a..e50b135d0b 100644
--- a/lib/6to5/transformation/transformers/es7-array-comprehension.js
+++ b/lib/6to5/transformation/transformers/es7-array-comprehension.js
@@ -5,7 +5,7 @@ var t                  = require("../../types");
 
 exports.experimental = true;
 
-var build = function (node, parent, file, scope) {
+var build = function (node, parent, scope, context, file) {
   var uid = scope.generateUidBasedOnNode(parent, file);
 
   var container = util.template("array-comprehension-container", {
@@ -34,8 +34,8 @@ var build = function (node, parent, file, scope) {
   return container;
 };
 
-exports.ComprehensionExpression = function (node, parent, file, scope) {
+exports.ComprehensionExpression = function (node, parent, scope, context, file) {
   if (node.generator) return;
 
-  return build(node, parent, file, scope);
+  return build(node, parent, scope, context, file);
 };
diff --git a/lib/6to5/transformation/transformers/es7-object-spread.js b/lib/6to5/transformation/transformers/es7-object-spread.js
index a9ffecaf03..083bbdc166 100644
--- a/lib/6to5/transformation/transformers/es7-object-spread.js
+++ b/lib/6to5/transformation/transformers/es7-object-spread.js
@@ -4,7 +4,7 @@ var t = require("../../types");
 
 exports.experimental = true;
 
-exports.ObjectExpression = function (node, parent, file) {
+exports.ObjectExpression = function (node, parent, scope, context, file) {
   var hasSpread = false;
   var i;
   var prop;
diff --git a/lib/6to5/transformation/transformers/optional-async-to-generator.js b/lib/6to5/transformation/transformers/optional-async-to-generator.js
index 143445a9c2..d6f952783c 100644
--- a/lib/6to5/transformation/transformers/optional-async-to-generator.js
+++ b/lib/6to5/transformation/transformers/optional-async-to-generator.js
@@ -5,7 +5,7 @@ exports.optional = true;
 
 exports.manipulateOptions = bluebirdCoroutines.manipulateOptions;
 
-exports.Function = function (node, parent, file) {
+exports.Function = function (node, parent, scope, context, file) {
   if (!node.async || node.generator) return;
 
   return remapAsyncToGenerator(node, file.addHelper("async-to-generator"));
diff --git a/lib/6to5/transformation/transformers/optional-bluebird-coroutines.js b/lib/6to5/transformation/transformers/optional-bluebird-coroutines.js
index 5338fa1e1c..73b9db1fd7 100644
--- a/lib/6to5/transformation/transformers/optional-bluebird-coroutines.js
+++ b/lib/6to5/transformation/transformers/optional-bluebird-coroutines.js
@@ -9,7 +9,7 @@ exports.manipulateOptions = function (opts) {
 exports.optional = true;
 
 
-exports.Function = function (node, parent, file) {
+exports.Function = function (node, parent, scope, context, file) {
   if (!node.async || node.generator) return;
 
   return remapAsyncToGenerator(
diff --git a/lib/6to5/transformation/transformers/optional-core-aliasing.js b/lib/6to5/transformation/transformers/optional-core-aliasing.js
index 3610ae8f62..d563bb619a 100644
--- a/lib/6to5/transformation/transformers/optional-core-aliasing.js
+++ b/lib/6to5/transformation/transformers/optional-core-aliasing.js
@@ -26,7 +26,7 @@ exports.ast = {
 
   exit: function (ast, file) {
     traverse(ast, {
-      enter: function (node, parent) {
+      enter: function (node, parent, scope, context) {
         var prop;
 
         if (t.isMemberExpression(node) && t.isReferenced(node, parent)) {
@@ -37,7 +37,7 @@ exports.ast = {
           if (!t.isReferenced(obj, node)) return;
 
           if (!node.computed && coreHas(obj) && _.has(core[obj.name], prop.name)) {
-            this.skip();
+            context.skip();
             return t.prependToMemberExpression(node, file._coreId);
           }
         } else if (t.isIdentifier(node) && !t.isMemberExpression(parent) && t.isReferenced(node, parent) && _.contains(ALIASABLE_CONSTRUCTORS, node.name)) {
diff --git a/lib/6to5/transformation/transformers/optional-proto-to-assign.js b/lib/6to5/transformation/transformers/optional-proto-to-assign.js
index e3f0a78022..73a9c8167d 100644
--- a/lib/6to5/transformation/transformers/optional-proto-to-assign.js
+++ b/lib/6to5/transformation/transformers/optional-proto-to-assign.js
@@ -17,7 +17,7 @@ var buildDefaultsCallExpression = function (expr, ref, file) {
 exports.optional = true;
 exports.secondPass = true;
 
-exports.AssignmentExpression = function (node, parent, file, scope) {
+exports.AssignmentExpression = function (node, parent, scope, context, file) {
   if (t.isExpressionStatement(parent)) return;
   if (!isProtoAssignmentExpression(node)) return;
 
@@ -32,7 +32,7 @@ exports.AssignmentExpression = function (node, parent, file, scope) {
   return t.toSequenceExpression(nodes);
 };
 
-exports.ExpressionStatement = function (node, parent, file) {
+exports.ExpressionStatement = function (node, parent, scope, context, file) {
   var expr = node.expression;
   if (!t.isAssignmentExpression(expr, { operator: "=" })) return;
 
@@ -41,7 +41,7 @@ exports.ExpressionStatement = function (node, parent, file) {
   }
 };
 
-exports.ObjectExpression = function (node, parent, file) {
+exports.ObjectExpression = function (node, parent, scope, context, file) {
   var proto;
 
   for (var i = 0; i < node.properties.length; i++) {
diff --git a/lib/6to5/transformation/transformers/optional-typeof-symbol.js b/lib/6to5/transformation/transformers/optional-typeof-symbol.js
index 36b8458936..1c1aed8cc1 100644
--- a/lib/6to5/transformation/transformers/optional-typeof-symbol.js
+++ b/lib/6to5/transformation/transformers/optional-typeof-symbol.js
@@ -2,8 +2,8 @@ var t = require("../../types");
 
 exports.optional = true;
 
-exports.UnaryExpression = function (node, parent, file) {
-  this.skip();
+exports.UnaryExpression = function (node, parent, scope, context, file) {
+  context.skip();
 
   if (node.operator === "typeof") {
     var call = t.callExpression(file.addHelper("typeof"), [node.argument]);
diff --git a/lib/6to5/transformation/transformers/playground-memoization-operator.js b/lib/6to5/transformation/transformers/playground-memoization-operator.js
index 1f5fa4bb9f..1bd6d004ee 100644
--- a/lib/6to5/transformation/transformers/playground-memoization-operator.js
+++ b/lib/6to5/transformation/transformers/playground-memoization-operator.js
@@ -48,7 +48,7 @@ var buildAssignment = function (expr, obj, prop) {
   return t.assignmentExpression("=", buildAbsoluteRef(expr.left, obj, prop), expr.right);
 };
 
-exports.ExpressionStatement = function (node, parent, file, scope) {
+exports.ExpressionStatement = function (node, parent, scope, context, file) {
   var expr = node.expression;
   if (!isMemo(expr)) return;
 
@@ -66,7 +66,7 @@ exports.ExpressionStatement = function (node, parent, file, scope) {
   return nodes;
 };
 
-exports.AssignmentExpression = function (node, parent, file, scope) {
+exports.AssignmentExpression = function (node, parent, scope, context, file) {
   if (t.isExpressionStatement(parent)) return;
   if (!isMemo(node)) return;
 
diff --git a/lib/6to5/transformation/transformers/playground-method-binding.js b/lib/6to5/transformation/transformers/playground-method-binding.js
index 6c6bd9e37b..4f3fe3bb51 100644
--- a/lib/6to5/transformation/transformers/playground-method-binding.js
+++ b/lib/6to5/transformation/transformers/playground-method-binding.js
@@ -1,6 +1,6 @@
 var t = require("../../types");
 
-exports.BindMemberExpression = function (node, parent, file, scope) {
+exports.BindMemberExpression = function (node, parent, scope, context, file) {
   var object = node.object;
   var prop   = node.property;
 
@@ -22,7 +22,7 @@ exports.BindMemberExpression = function (node, parent, file, scope) {
   }
 };
 
-exports.BindFunctionExpression = function (node, parent, file, scope) {
+exports.BindFunctionExpression = function (node, parent, scope, context, file) {
   var buildCall = function (args) {
     var param = file.generateUidIdentifier("val", scope);
     return t.functionExpression(null, [param], t.blockStatement([
diff --git a/lib/6to5/transformation/transformers/playground-object-getter-memoization.js b/lib/6to5/transformation/transformers/playground-object-getter-memoization.js
index 9c3f0bb6d0..08af63ea57 100644
--- a/lib/6to5/transformation/transformers/playground-object-getter-memoization.js
+++ b/lib/6to5/transformation/transformers/playground-object-getter-memoization.js
@@ -2,7 +2,7 @@ var traverse = require("../../traverse");
 var t        = require("../../types");
 
 exports.Property =
-exports.MethodDefinition = function (node, parent, file) {
+exports.MethodDefinition = function (node, parent, scope, context, file) {
   if (node.kind !== "memo") return;
   node.kind = "get";
 
diff --git a/lib/6to5/transformation/transformers/react.js b/lib/6to5/transformation/transformers/react.js
index 4dc53db287..76592d97c2 100644
--- a/lib/6to5/transformation/transformers/react.js
+++ b/lib/6to5/transformation/transformers/react.js
@@ -15,7 +15,7 @@ exports.XJSIdentifier = function (node) {
   }
 };
 
-exports.XJSNamespacedName = function (node, parent, file) {
+exports.XJSNamespacedName = function (node, parent, scope, context, file) {
   throw file.errorWithNode(node, "Namespace tags are not supported. ReactJSX is not XML.");
 };
 
@@ -42,7 +42,7 @@ var isCompatTag = function(tagName) {
 };
 
 exports.XJSOpeningElement = {
-  exit: function (node, parent, file) {
+  exit: function (node, parent, scope, context, file) {
     var reactCompat = file.opts.reactCompat;
     var tagExpr = node.name;
     var args = [];
diff --git a/lib/6to5/transformation/transformers/spec-no-for-in-of-assignment.js b/lib/6to5/transformation/transformers/spec-no-for-in-of-assignment.js
index 5af12108f1..0b00e88f9d 100644
--- a/lib/6to5/transformation/transformers/spec-no-for-in-of-assignment.js
+++ b/lib/6to5/transformation/transformers/spec-no-for-in-of-assignment.js
@@ -1,7 +1,7 @@
 var t = require("../../types");
 
 exports.ForInStatement =
-exports.ForOfStatement = function (node, parent, file) {
+exports.ForOfStatement = function (node, parent, scope, context, file) {
   var left = node.left;
   if (t.isVariableDeclaration(left)) {
     var declar = left.declarations[0];
diff --git a/lib/6to5/transformation/transformers/spec-setters.js b/lib/6to5/transformation/transformers/spec-setters.js
index 30b404ed1e..54d88827aa 100644
--- a/lib/6to5/transformation/transformers/spec-setters.js
+++ b/lib/6to5/transformation/transformers/spec-setters.js
@@ -1,5 +1,5 @@
 exports.MethodDefinition =
-exports.Property = function (node, parent, file) {
+exports.Property = function (node, parent, scope, context, file) {
   if (node.kind === "set" && node.value.params.length !== 1) {
     throw file.errorWithNode(node.value, "Setters must have only one parameter");
   }
diff --git a/lib/6to5/traverse/index.js b/lib/6to5/traverse/index.js
index 5667ce1f46..7307a7665d 100644
--- a/lib/6to5/traverse/index.js
+++ b/lib/6to5/traverse/index.js
@@ -1,14 +1,18 @@
 module.exports = traverse;
 
+/* jshint maxparams:7 */
+
 var Scope = require("./scope");
 var t     = require("../types");
 var _     = require("lodash");
 
-function TraversalContext(previousContext) {
+function noop() { }
+
+function TraversalContext() {
   this.didSkip = false;
   this.didRemove = false;
   this.didStop = false;
-  this.didFlatten = previousContext ? previousContext.didFlatten : false;
+  this.didFlatten = false;
 }
 
 TraversalContext.prototype.flatten = function () {
@@ -17,7 +21,7 @@ TraversalContext.prototype.flatten = function () {
 
 TraversalContext.prototype.remove = function () {
   this.didRemove = true;
-  this.skip();
+  this.didSkip = true;
 };
 
 TraversalContext.prototype.skip = function () {
@@ -26,13 +30,16 @@ TraversalContext.prototype.skip = function () {
 
 TraversalContext.prototype.stop = function () {
   this.didStop = true;
-  this.skip();
+  this.didSkip = true;
 };
 
-TraversalContext.prototype.maybeReplace = function (result, obj, key, node) {
-  if (result === false) return node;
-  if (result == null) return node;
+TraversalContext.prototype.reset = function () {
+  this.didSkip = false;
+  this.didStop = false;
+  this.didRemove = false;
+};
 
+function replaceNode(obj, key, node, result) {
   var isArray = Array.isArray(result);
 
   // inherit comments from original node to the first replacement node
@@ -41,7 +48,7 @@ TraversalContext.prototype.maybeReplace = function (result, obj, key, node) {
   if (inheritTo) t.inheritsComments(inheritTo, node);
 
   // replace the node
-  node = obj[key] = result;
+  obj[key] = result;
 
   // we're replacing a statement or block node with an array of statements so we better
   // ensure that it's a block
@@ -50,104 +57,139 @@ TraversalContext.prototype.maybeReplace = function (result, obj, key, node) {
   }
 
   if (isArray) {
-    this.flatten();
+    return true;
+  }
+}
+
+TraversalContext.prototype.enterNode = function (obj, key, node, enter, parent, scope, state) {
+  var result = enter(node, parent, scope, this, state);
+  var flatten = false;
+
+  if (result) {
+    flatten = replaceNode(obj, key, node, result);
+    node = result;
+
+    if (flatten) {
+      this.didFlatten = true;
+    }
+  }
+
+  if (this.didRemove) {
+    obj[key] = null;
+    this.didFlatten = true;
   }
 
   return node;
 };
 
-TraversalContext.prototype.visit = function (obj, key, opts, scope, parent) {
-  var node = obj[key];
-  if (!node) return;
+TraversalContext.prototype.exitNode = function (obj, key, node, exit, parent, scope, state) {
+  var result = exit(node, parent, scope, this, state);
+  var flatten = false;
 
-  // type is blacklisted
-  if (opts.blacklist && opts.blacklist.indexOf(node.type) > -1) return;
+  if (result) {
+    flatten = replaceNode(obj, key, node, result);
+    node = result;
 
-  var result;
-  var ourScope = scope;
-  if (t.isScope(node)) ourScope = new Scope(node, scope);
-
-  // enter
-  if (opts.enter) {
-    result = opts.enter.call(this, node, parent, ourScope);
-    node = this.maybeReplace(result, obj, key, node);
-
-    if (this.didRemove) {
-      obj[key] = null;
-      this.flatten();
+    if (flatten) {
+      this.didFlatten = true;
     }
-
-    // stop traversal
-    if (this.didSkip) return;
   }
 
-  // traverse node
-  traverse(node, opts, ourScope);
-
-  // exit
-  if (opts.exit) {
-    result = opts.exit.call(this, node, parent, ourScope);
-    node = this.maybeReplace(result, obj, key, node);
-  }
+  return node;
 };
 
-function traverse(parent, opts, scope) {
-  // falsy node
-  if (!parent) return;
+TraversalContext.prototype.visitNode = function (obj, key, opts, scope, parent, state) {
+  this.reset();
 
-  // array of nodes
-  if (Array.isArray(parent)) {
-    for (var i = 0; i < parent.length; i++)
-      traverse(parent[i], opts, scope);
+  var node = obj[key];
+
+  // type is blacklisted
+  if (opts.blacklist && opts.blacklist.indexOf(node.type) > -1)
+    return;
+
+  var ourScope = scope;
+  if (t.isScope(node))
+    ourScope = new Scope(node, scope);
+
+  node = this.enterNode(obj, key, node, opts.enter, parent, ourScope, state);
+
+  if (this.didSkip)
+    return this.didStop;
+
+  traverseNode(node, opts, ourScope, state);
+  this.exitNode(obj, key, node, opts.exit, parent, ourScope, state);
+
+  return this.didStop;
+};
+
+TraversalContext.prototype.visit = function (node, key, opts, scope, state) {
+  var nodes = node[key];
+  if (!nodes) return;
+
+  if (!Array.isArray(nodes)) {
+    return this.visitNode(node, key, opts, scope, node, state);
+  }
+
+  if (nodes.length === 0) {
     return;
   }
 
-  // unknown node type to traverse
-  var keys = t.VISITOR_KEYS[parent.type];
+  for (var k = 0; k < nodes.length; k++) {
+    if (nodes[k] && this.visitNode(nodes, k, opts, scope, node, state))
+      return true;
+  }
+
+  if (this.didFlatten) {
+    node[key] = _.flatten(node[key]);
+
+    if (key === "body") {
+      // we can safely compact this
+      node[key] = _.compact(node[key]);
+    }
+  }
+};
+
+function traverseNode(node, opts, scope, state) {
+  var keys = t.VISITOR_KEYS[node.type];
   if (!keys) return;
 
-  opts = opts || {};
-  var context = null;
-
+  var context = new TraversalContext();
   for (var j = 0; j < keys.length; j++) {
-    var key = keys[j];
-    var nodes = parent[key];
-    if (!nodes) continue;
+    if (context.visit(node, keys[j], opts, scope, state))
+      return;
+  }
+}
 
-    if (Array.isArray(nodes)) {
-      for (var k = 0; k < nodes.length; k++) {
-        context = new TraversalContext(context);
-        context.visit(nodes, k, opts, scope, parent);
-        if (context.didStop) return;
-      }
+function traverse(parent, opts, scope, state) {
+  // falsy node
+  if (!parent) return;
 
-      if (context && context.didFlatten) {
-        parent[key] = _.flatten(parent[key]);
+  if (!opts) opts = {};
+  if (!opts.enter) opts.enter = noop;
+  if (!opts.exit) opts.exit = noop;
 
-        if (key === "body") {
-          // we can safely compact this
-          parent[key] = _.compact(parent[key]);
-        }
-      }
-    } else {
-      context = new TraversalContext(context);
-      context.visit(parent, key, opts, scope, parent);
-      if (context.didStop) return;
-    }
+  // array of nodes
+  if (!Array.isArray(parent)) {
+    traverseNode(parent, opts, scope, state);
+    return;
+  }
+
+  for (var i = 0; i < parent.length; i++) {
+    traverseNode(parent[i], opts, scope, state);
   }
 }
 
 traverse.removeProperties = function (tree) {
   var clear = function (node) {
-    delete node._declarations;
-    delete node.extendedRange;
-    delete node._scopeInfo;
-    delete node.tokens;
-    delete node.range;
-    delete node.start;
-    delete node.end;
-    delete node.loc;
-    delete node.raw;
+    node._declarations = null;
+    node.extendedRange = null;
+    node._scopeInfo = null;
+    node.tokens = null;
+    node.range = null;
+    node.start = null;
+    node.end = null;
+    node.loc = null;
+    node.raw = null;
 
     clearComments(node.trailingComments);
     clearComments(node.leadingComments);
@@ -166,23 +208,25 @@ traverse.removeProperties = function (tree) {
 traverse.hasType = function (tree, type, blacklistTypes) {
   blacklistTypes = [].concat(blacklistTypes || []);
 
-  var has = false;
-
   // the node we're searching in is blacklisted
   if (_.contains(blacklistTypes, tree.type)) return false;
 
   // the type we're looking for is the same as the passed node
   if (tree.type === type) return true;
 
+  var state = {
+    has: false
+  };
+
   traverse(tree, {
     blacklist: blacklistTypes,
-    enter: function (node) {
+    enter: function (node, parent, scope, context, state) {
       if (node.type === type) {
-        has = true;
-        this.skip();
+        state.has = true;
+        context.skip();
       }
     }
-  });
+  }, null, state);
 
-  return has;
+  return state.has;
 };
diff --git a/lib/6to5/traverse/scope.js b/lib/6to5/traverse/scope.js
index f02803c886..320728c059 100644
--- a/lib/6to5/traverse/scope.js
+++ b/lib/6to5/traverse/scope.js
@@ -159,8 +159,13 @@ Scope.prototype.getInfo = function () {
   // Program, Function - var variables
 
   if (t.isProgram(block) || t.isFunction(block)) {
+    var state = {
+      blockId: block.id,
+      add: add
+    };
+
     traverse(block, {
-      enter: function (node, parent, scope) {
+      enter: function (node, parent, scope, context, state) {
         if (t.isFor(node)) {
           _.each(FOR_KEYS, function (key) {
             var declar = node[key];
@@ -170,22 +175,22 @@ Scope.prototype.getInfo = function () {
 
         // this block is a function so we'll stop since none of the variables
         // declared within are accessible
-        if (t.isFunction(node)) return this.skip();
+        if (t.isFunction(node)) return context.skip();
 
         // function identifier doesn't belong to this scope
-        if (block.id && node === block.id) return;
+        if (state.blockId && node === state.blockId) return;
 
         if (t.isIdentifier(node) && t.isReferenced(node, parent) && !scope.has(node.name)) {
-          add(node, true);
+          state.add(node, true);
         }
 
         // we've ran into a declaration!
         // we'll let the BlockStatement scope deal with `let` declarations unless
         if (t.isDeclaration(node) && !t.isLet(node)) {
-          add(node);
+          state.add(node);
         }
       }
-    }, this);
+    }, this, state);
   }
 
   // Function - params, rest
diff --git a/lib/6to5/types/index.js b/lib/6to5/types/index.js
index 2891d2df82..9155d41bd4 100644
--- a/lib/6to5/types/index.js
+++ b/lib/6to5/types/index.js
@@ -1,5 +1,6 @@
-var esutils = require("esutils");
-var _       = require("lodash");
+var esutils          = require("esutils");
+var _                = require("lodash");
+var toFastProperties = require("../to-fast-properties");
 
 var t = exports;
 
@@ -573,3 +574,6 @@ t.getSpecifierName = function (specifier) {
 t.isSpecifierDefault = function (specifier) {
   return t.isIdentifier(specifier.id) && specifier.id.name === "default";
 };
+
+toFastProperties(t);
+toFastProperties(t.VISITOR_KEYS);
\ No newline at end of file
diff --git a/lib/6to5/util.js b/lib/6to5/util.js
index 66af587e4f..626d06305d 100644
--- a/lib/6to5/util.js
+++ b/lib/6to5/util.js
@@ -129,6 +129,14 @@ exports.buildDefineProperties = function (mutatorMap) {
   return objExpr;
 };
 
+var templateTraverser = {
+  enter: function (node, parent, scope, context, nodes) {
+    if (t.isIdentifier(node) && _.has(nodes, node.name)) {
+      return nodes[node.name];
+    }
+  }
+};
+
 exports.template = function (name, nodes, keepExpression) {
   var template = exports.templates[name];
   if (!template) throw new ReferenceError("unknown template " + name);
@@ -141,13 +149,7 @@ exports.template = function (name, nodes, keepExpression) {
   template = _.cloneDeep(template);
 
   if (!_.isEmpty(nodes)) {
-    traverse(template, {
-      enter: function (node) {
-        if (t.isIdentifier(node) && _.has(nodes, node.name)) {
-          return nodes[node.name];
-        }
-      }
-    });
+    traverse(template, templateTraverser, null, nodes);
   }
 
   var node = template.body[0];