diff --git a/src/babel/transformation/file/index.js b/src/babel/transformation/file/index.js
index 1ea0385b03..a16be564ee 100644
--- a/src/babel/transformation/file/index.js
+++ b/src/babel/transformation/file/index.js
@@ -462,7 +462,12 @@ export default class File {
   }
 
   _addAst(ast) {
-    this.path  = NodePath.get(null, ast, ast, "program", this).setContext(null, this);
+    this.path  = NodePath.get({
+      parentPath: null,
+      parent: ast,
+      container: ast,
+      key: "program"
+    }).setContext(null, this);
     this.scope = this.path.scope;
     this.ast   = ast;
   }
diff --git a/src/babel/traversal/context.js b/src/babel/traversal/context.js
index c15004a9f6..9ed3481b5f 100644
--- a/src/babel/traversal/context.js
+++ b/src/babel/traversal/context.js
@@ -14,15 +14,21 @@ export default class TraversalContext {
     return !!(this.opts.enter || this.opts.exit || this.opts[node.type] || (keys && keys.length));
   }
 
-  create(node, obj, key) {
-    var path = NodePath.get(this.parentPath, node, obj, key);
+  create(node, obj, key, containerKey) {
+    var path = NodePath.get({
+      parentPath: this.parentPath,
+      parent: node,
+      container: obj,
+      key: key,
+      containerKey: containerKey
+    });
     path.unshiftContext(this);
     return path;
   }
 
-  visitMultiple(nodes, node) {
+  visitMultiple(container, parent, containerKey) {
     // nothing to traverse!
-    if (nodes.length === 0) return false;
+    if (container.length === 0) return false;
 
     var visited = [];
 
@@ -30,16 +36,16 @@ export default class TraversalContext {
     var stop  = false;
 
     // build up initial queue
-    for (let i = 0; i < nodes.length; i++) {
-      var self = nodes[i];
+    for (let key = 0; key < container.length; key++) {
+      var self = container[key];
       if (self && this.shouldVisit(self)) {
-        queue.push(this.create(node, nodes, i));
+        queue.push(this.create(parent, container, key, containerKey));
       }
     }
 
     // visit the queue
     for (let path of (queue: Array)) {
-      path.update();
+      path.resync();
 
       if (visited.indexOf(path.node) >= 0) continue;
       visited.push(path.node);
diff --git a/src/babel/traversal/path/context.js b/src/babel/traversal/path/context.js
index ba19552d1c..41e18b6870 100644
--- a/src/babel/traversal/path/context.js
+++ b/src/babel/traversal/path/context.js
@@ -108,6 +108,7 @@ export function setScope(file?) {
 
   var target = this.context || this.parentPath;
   this.scope = NodePath.getScope(this, target && target.scope, file);
+  if (this.scope) this.scope.init();
 }
 
 /**
@@ -137,7 +138,14 @@ export function setContext(context, file) {
  * Description
  */
 
-export function update() {
+export function resync() {
+  if (this.removed) return;
+
+  this._resyncContainer();
+  this._resyncKey();
+}
+
+export function _resyncKey() {
   if (this.node === this.container[this.key]) return;
 
   // grrr, path key is out of sync. this is likely due to a modification to the AST
@@ -160,6 +168,17 @@ export function update() {
   throw new Error(messages.get("lostTrackNodePath"));
 }
 
+export function _resyncContainer() {
+  var containerKey = this.containerKey;
+  var parentPath   = this.parentPath;
+  if (!containerKey || !parentPath) return;
+
+  var newContainer = parentPath.node[containerKey];
+  if (!newContainer || this.container === newContainer) return;
+
+  this.container = newContainer;
+}
+
 /**
  * Description
  */
diff --git a/src/babel/traversal/path/family.js b/src/babel/traversal/path/family.js
index 023da87e9f..cfba7de496 100644
--- a/src/babel/traversal/path/family.js
+++ b/src/babel/traversal/path/family.js
@@ -55,7 +55,13 @@ export function getCompletionRecords(): Array<NodePath> {
  */
 
 export function getSibling(key) {
-  return NodePath.get(this.parentPath, this.parent, this.container, key, this.file);
+  return NodePath.get({
+    parentPath: this.parentPath,
+    parent: this.parent,
+    container: this.container,
+    containerKey: this.containerKey,
+    key: key
+  });
 }
 
 /**
@@ -82,10 +88,21 @@ export function _getKey(key) {
   if (Array.isArray(container)) {
     // requested a container so give them all the paths
     return container.map((_, i) => {
-      return NodePath.get(this, node, container, i).setContext();
+      return NodePath.get({
+        containerKey: key,
+        parentPath: this,
+        parent: node,
+        container: container,
+        key: i
+      }).setContext();
     });
   } else {
-    return NodePath.get(this, node, node, key).setContext();
+    return NodePath.get({
+      parentPath: this,
+      parent: node,
+      container: node,
+      key: key
+    }).setContext();
   }
 }
 
diff --git a/src/babel/traversal/path/index.js b/src/babel/traversal/path/index.js
index 5044ded011..601cbb1832 100644
--- a/src/babel/traversal/path/index.js
+++ b/src/babel/traversal/path/index.js
@@ -5,18 +5,19 @@ import Scope from "../scope";
 import * as t from "../../types";
 
 export default class NodePath {
-  constructor(parent, container) {
-    this.container = container;
-    this.contexts  = [];
-    this.parent    = parent;
-    this.data      = {};
+  constructor(parent, container, containerKey) {
+    this.containerKey = containerKey;
+    this.container    = container;
+    this.contexts     = [];
+    this.parent       = parent;
+    this.data         = {};
   }
 
   /**
    * Description
    */
 
-  static get(parentPath: NodePath, parent, container, key) {
+  static get({ parentPath, parent, container, containerKey, key }) {
     var targetNode = container[key];
     var paths = container._paths = container._paths || [];
     var path;
@@ -30,7 +31,7 @@ export default class NodePath {
     }
 
     if (!path) {
-      path = new NodePath(parent, container);
+      path = new NodePath(parent, container, containerKey);
       paths.push(path);
     }
 
diff --git a/src/babel/traversal/path/modification.js b/src/babel/traversal/path/modification.js
index c3bf91fca6..466d15d73a 100644
--- a/src/babel/traversal/path/modification.js
+++ b/src/babel/traversal/path/modification.js
@@ -40,11 +40,17 @@ export function _containerInsert(from, nodes) {
     this.container.splice(to, 0, node);
 
     if (this.context) {
-      var path = this.context.create(this.parent, this.container, to);
+      var path = this.context.create(this.parent, this.container, to, this.containerKey);
       paths.push(path);
       this.queueNode(path);
     } else {
-      paths.push(NodePath.get(this, node, this.container, to));
+      paths.push(NodePath.get({
+        parentPath: this,
+        parent: node,
+        container: this.container,
+        containerKey: this.containerKey,
+        key: to
+      }));
     }
   }
 
@@ -145,7 +151,13 @@ export function unshiftContainer(containerKey, nodes) {
   // doesn't matter, our nodes will be inserted anyway
 
   var container = this.node[containerKey];
-  var path      = NodePath.get(this, this.node, container, 0);
+  var path      = NodePath.get({
+    parentPath: this,
+    parent: this.node,
+    container: container,
+    containerKey,
+    key: 0
+  });
 
   return path.insertBefore(nodes);
 }
@@ -162,7 +174,13 @@ export function pushContainer(containerKey, nodes) {
 
   var container = this.node[containerKey];
   var i         = container.length;
-  var path      = NodePath.get(this, this.node, container, i);
+  var path      = NodePath.get({
+    parentPath: this,
+    parent: this.node,
+    container: container,
+    containerKey,
+    key: i
+  });
 
   return path.replaceWith(nodes, true);
 }
diff --git a/src/babel/traversal/path/removal.js b/src/babel/traversal/path/removal.js
index be7b9ba55e..6e832f0cb8 100644
--- a/src/babel/traversal/path/removal.js
+++ b/src/babel/traversal/path/removal.js
@@ -5,18 +5,23 @@ import * as removalHooks from "./lib/removal-hooks";
  */
 
 export function remove() {
-  if (this._callRemovalHooks("pre")) return;
+  this.resync();
+
+  if (this._callRemovalHooks("pre")) {
+    this._markRemoved();
+    return;
+  }
 
   this.shareCommentsWithSiblings();
   this._remove();
-  this.removed = true;
+  this._markRemoved();
 
   this._callRemovalHooks("post");
 }
 
 export function _callRemovalHooks(position) {
   for (var fn of (removalHooks[position]: Array)) {
-    if (fn(this, this.parentPath)) return;
+    if (fn(this, this.parentPath)) return true;
   }
 }
 
@@ -27,7 +32,11 @@ export function _remove() {
   } else {
     this.container[this.key] = null;
   }
+}
+
+export function _markRemoved() {
   this.node = null;
+  this.removed = true;
 }
 
 /**
diff --git a/src/babel/traversal/path/replacement.js b/src/babel/traversal/path/replacement.js
index ef7069cd5b..4e2e7c8ff7 100644
--- a/src/babel/traversal/path/replacement.js
+++ b/src/babel/traversal/path/replacement.js
@@ -35,6 +35,8 @@ var hoistVariablesVisitor = {
  */
 
 export function replaceWithMultiple(nodes: Array<Object>) {
+  this.resync();
+
   nodes = this._verifyNodeList(nodes);
   t.inheritsComments(nodes[0], this.node);
   this.node = this.container[this.key] = null;
@@ -47,6 +49,8 @@ export function replaceWithMultiple(nodes: Array<Object>) {
  */
 
 export function replaceWithSourceString(replacement) {
+  this.resync();
+
   try {
     replacement = `(${replacement})`;
     replacement = parse(replacement);
@@ -69,6 +73,8 @@ export function replaceWithSourceString(replacement) {
  */
 
 export function replaceWith(replacement, whateverAllowed) {
+  this.resync();
+
   if (this.removed) {
     throw new Error("You can't replace this node, we've already removed it");
   }
@@ -129,6 +135,8 @@ export function replaceWith(replacement, whateverAllowed) {
  */
 
 export function replaceExpressionWithStatements(nodes: Array) {
+  this.resync();
+
   var toSequenceExpression = t.toSequenceExpression(nodes, this.scope);
 
   if (toSequenceExpression) {
@@ -167,6 +175,8 @@ export function replaceExpressionWithStatements(nodes: Array) {
  */
 
 export function replaceInline(nodes) {
+  this.resync();
+
   if (Array.isArray(nodes)) {
     if (Array.isArray(this.container)) {
       nodes = this._verifyNodeList(nodes);
diff --git a/src/babel/traversal/scope/index.js b/src/babel/traversal/scope/index.js
index 0f7e80e551..15c2c8b64d 100644
--- a/src/babel/traversal/scope/index.js
+++ b/src/babel/traversal/scope/index.js
@@ -146,8 +146,6 @@ export default class Scope {
     this.parentBlock = path.parent;
     this.block       = path.node;
     this.path        = path;
-
-    this.crawl();
   }
 
   static globals = flatten([globals.builtin, globals.browser, globals.node].map(Object.keys));
@@ -552,11 +550,21 @@ export default class Scope {
     if (t.isIdentifier(node)) {
       var bindingInfo = this.getBinding(node.name);
       return bindingInfo && bindingInfo.constant;
+    } else if (t.isClass(node)) {
+      return !node.superClass;
     } else {
       return t.isPure(node);
     }
   }
 
+  /**
+   * Description
+   */
+
+  init() {
+    if (!this.references) this.crawl();
+  }
+
   /**
    * Description
    */
@@ -613,7 +621,7 @@ export default class Scope {
       for (let param of (params: Array)) {
         this.registerBinding("param", param);
       }
-      this.traverse(path.get("body").node, blockVariableVisitor, this);
+      path.get("body").traverse(blockVariableVisitor, this);
     }
 
     // Program, Function - var variables
diff --git a/src/babel/types/alias-keys.json b/src/babel/types/alias-keys.json
index 620f8903b5..07fc4000e9 100644
--- a/src/babel/types/alias-keys.json
+++ b/src/babel/types/alias-keys.json
@@ -41,8 +41,8 @@
   "SpreadProperty":  ["UnaryLike"],
   "SpreadElement":   ["UnaryLike"],
 
-  "ClassDeclaration": ["Scopable", "Class", "Pure", "Statement", "Declaration"],
-  "ClassExpression":  ["Scopable", "Class", "Pure", "Expression"],
+  "ClassDeclaration": ["Scopable", "Class", "Statement", "Declaration"],
+  "ClassExpression":  ["Scopable", "Class", "Expression"],
 
   "ForOfStatement": ["Scopable", "Statement", "For", "Loop"],
   "ForInStatement": ["Scopable", "Statement", "For", "Loop"],