diff --git a/src/babel/transformation/file/index.js b/src/babel/transformation/file/index.js
index 75e844f61a..84dd7d66d5 100644
--- a/src/babel/transformation/file/index.js
+++ b/src/babel/transformation/file/index.js
@@ -508,7 +508,7 @@ export default class File {
     this.log.debug("End set AST");
 
     this.log.debug("Start prepass");
-    //this.checkPath(this.path);
+    this.checkPath(this.path);
     this.log.debug("End prepass");
 
     this.log.debug("Start module formatter init");
diff --git a/src/babel/transformation/helpers/build-binary-assignment-operator-transformer.js b/src/babel/transformation/helpers/build-binary-assignment-operator-transformer.js
index 04ffc4c1b3..45a6d812c5 100644
--- a/src/babel/transformation/helpers/build-binary-assignment-operator-transformer.js
+++ b/src/babel/transformation/helpers/build-binary-assignment-operator-transformer.js
@@ -10,6 +10,10 @@ export default function (exports, opts) {
     return t.assignmentExpression("=", left, right);
   };
 
+  exports.shouldVisit = function (node) {
+    return node.operator && (node.operator === opts.operator || node.operator === opts.operator + "=");
+  };
+
   exports.ExpressionStatement = function (node, parent, scope, file) {
     // hit the `AssignmentExpression` one below
     if (this.isCompletionRecord()) return;
diff --git a/src/babel/transformation/helpers/memoise-decorators.js b/src/babel/transformation/helpers/memoise-decorators.js
index 9e012bdf72..25d1032b1d 100644
--- a/src/babel/transformation/helpers/memoise-decorators.js
+++ b/src/babel/transformation/helpers/memoise-decorators.js
@@ -26,7 +26,11 @@ export default function (decorators, scope) {
       [ref]
     ));
 
-    decorator.expression = t.sequenceExpression(nodes);
+    if (nodes.length === 1) {
+      decorator.expression = nodes[0];
+    } else {
+      decorator.expression = t.sequenceExpression(nodes);
+    }
   }
 
   return decorators;
diff --git a/src/babel/transformation/helpers/name-method.js b/src/babel/transformation/helpers/name-method.js
index 0dc3628a9d..6e2845a274 100644
--- a/src/babel/transformation/helpers/name-method.js
+++ b/src/babel/transformation/helpers/name-method.js
@@ -39,7 +39,6 @@ var wrap = function (state, method, id, scope) {
     return template;
   } else {
     method.id = id;
-    return method;
   }
 };
 
@@ -96,7 +95,7 @@ export function custom(node, id, scope) {
 
 export function property(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
+  if (!t.isLiteral(key)) return; // we can't set a function id with this
 
   var name = t.toIdentifier(key.value);
   if (name === "eval" || name === "arguments") name = "_" + name;
@@ -109,7 +108,7 @@ export function property(node, file, scope) {
 
 export function bare(node, parent, scope) {
   // has an `id` so we don't need to infer one
-  if (node.id) return node;
+  if (node.id) return;
 
   var id;
   if (t.isProperty(parent) && parent.kind === "init" && (!parent.computed || t.isLiteral(parent.key))) {
@@ -119,7 +118,7 @@ export function bare(node, parent, scope) {
     // var foo = function () {};
     id = parent.id;
   } else {
-    return node;
+    return;
   }
 
   var name;
@@ -128,7 +127,7 @@ export function bare(node, parent, scope) {
   } else if (t.isIdentifier(id)) {
     name = id.name;
   } else {
-    return node;
+    return;
   }
 
   name = t.toIdentifier(name);
diff --git a/src/babel/transformation/transformer-pass.js b/src/babel/transformation/transformer-pass.js
index c6ce71f05a..81e03eda28 100644
--- a/src/babel/transformation/transformer-pass.js
+++ b/src/babel/transformation/transformer-pass.js
@@ -8,11 +8,12 @@ import traverse from "../traversal";
 
 export default class TransformerPass {
   constructor(file: File, transformer: Transformer) {
-    this.transformer = transformer;
-    this.handlers    = transformer.handlers;
-    this.skipKey     = transformer.skipKey;
-    this.file        = file;
-    this.ran         = false;
+    this.shouldTransform = !transformer.shouldVisit;
+    this.transformer     = transformer;
+    this.handlers        = transformer.handlers;
+    this.skipKey         = transformer.skipKey;
+    this.file            = file;
+    this.ran             = false;
   }
 
   canTransform(): boolean {
@@ -43,12 +44,14 @@ export default class TransformerPass {
   }
 
   checkPath(path: TraversalPath): boolean {
-    var shouldVisit = this.transformer.shouldVisit;
-    if (!shouldVisit) return;
+    if (this.shouldTransform || this.ran) return;
 
+    this.shouldTransform = this.transformer.shouldVisit(path.node);
   }
 
   transform() {
+    if (!this.shouldTransform) return;
+
     var file = this.file;
 
     file.log.debug(`Start transformer ${this.transformer.key}`);
diff --git a/src/babel/transformation/transformer.js b/src/babel/transformation/transformer.js
index 71b27a3986..361a329078 100644
--- a/src/babel/transformation/transformer.js
+++ b/src/babel/transformation/transformer.js
@@ -26,7 +26,6 @@ export default class Transformer {
     this.manipulateOptions = take("manipulateOptions");
     this.shouldVisit       = take("shouldVisit");
     this.metadata          = take("metadata") || {};
-    this.skipKey           = `transformer:${transformerKey}:skip`;
     this.parser            = take("parser");
     this.post              = take("post");
     this.pre               = take("pre");
@@ -48,7 +47,10 @@ export default class Transformer {
     if (!this.shouldVisit) {
       var types = Object.keys(this.handlers);
       this.shouldVisit = function (node) {
-        return types.indexOf(node.type) >= 0;
+        for (var i = 0; i < types.length; i++) {
+          if (node.type === types[i]) return true;
+        }
+        return false;
       };
     }
   }
@@ -79,10 +81,6 @@ export default class Transformer {
       transformer[type] = fns;
     });
 
-    transformer.shouldSkip = (path) => {
-      return path.getData(this.skipKey) === true;
-    };
-
     return transformer;
   }
 
diff --git a/src/babel/transformation/transformers/es6/classes.js b/src/babel/transformation/transformers/es6/classes.js
index 12fb1765fe..4dedf33981 100644
--- a/src/babel/transformation/transformers/es6/classes.js
+++ b/src/babel/transformation/transformers/es6/classes.js
@@ -245,7 +245,7 @@ class ClassTransformer {
       if (body.length === 1) return t.toExpression(body[0]);
     } else {
       // infer class name if this is a nameless class expression
-      constructor = nameMethod.bare(constructor, this.parent, this.scope);
+      constructor = nameMethod.bare(constructor, this.parent, this.scope) || constructor;
 
       body.unshift(t.variableDeclaration("var", [
         t.variableDeclarator(classRef, constructor)
diff --git a/src/babel/transformation/transformers/index.js b/src/babel/transformation/transformers/index.js
index 1ec845d14a..a6153cd1ba 100644
--- a/src/babel/transformation/transformers/index.js
+++ b/src/babel/transformation/transformers/index.js
@@ -115,6 +115,5 @@ export default {
   "utility.inlineExpressions":             require("./utility/inline-expressions"),
   "utility.deadCodeElimination":           require("./utility/dead-code-elimination"),
 
-  flow:                                    require("./other/flow"),
-  _cleanUp:                                require("./internal/cleanup")
+  flow:                                    require("./other/flow")
 };
diff --git a/src/babel/transformation/transformers/internal/cleanup.js b/src/babel/transformation/transformers/internal/cleanup.js
deleted file mode 100644
index c9f7ca4f97..0000000000
--- a/src/babel/transformation/transformers/internal/cleanup.js
+++ /dev/null
@@ -1,30 +0,0 @@
-export var SequenceExpression = {
-  exit(node) {
-    if (node.expressions.length === 1) {
-      return node.expressions[0];
-    } else if (!node.expressions.length) {
-      this.remove();
-    }
-  }
-};
-
-export var ExpressionStatement = {
-  exit(node) {
-    if (!node.expression) this.remove();
-  }
-};
-
-export var Binary = {
-  exit(node) {
-    var right = node.right;
-    var left  = node.left;
-
-    if (!left && !right) {
-      this.remove();
-    } else if (!left) {
-      return right;
-    } else if (!right) {
-      return left;
-    }
-  }
-};
diff --git a/src/babel/transformation/transformers/internal/module-formatter.js b/src/babel/transformation/transformers/internal/module-formatter.js
index 400f27e28a..92ef7baab2 100644
--- a/src/babel/transformation/transformers/internal/module-formatter.js
+++ b/src/babel/transformation/transformers/internal/module-formatter.js
@@ -1,6 +1,8 @@
 import * as strict from "../../helpers/strict";
 
 export function Program(program, parent, scope, file) {
+  this.stop();
+
   strict.wrap(program, function () {
     program.body = file.dynamicImports.concat(program.body);
   });
diff --git a/src/babel/transformation/transformers/other/flow.js b/src/babel/transformation/transformers/other/flow.js
index bb6bf4c393..b3a963e3cc 100644
--- a/src/babel/transformation/transformers/other/flow.js
+++ b/src/babel/transformation/transformers/other/flow.js
@@ -1,5 +1,9 @@
 import * as t from "../../../types";
 
+export function shouldVisit(node) {
+  return node.isType || node.optional || node.implements || node.typeAnnotation || t.isFlow(node);
+}
+
 export function Flow(node) {
   this.remove();
 }
diff --git a/src/babel/transformation/transformers/spec/block-scoped-functions.js b/src/babel/transformation/transformers/spec/block-scoped-functions.js
index ae16f05fcb..a1b17960f0 100644
--- a/src/babel/transformation/transformers/spec/block-scoped-functions.js
+++ b/src/babel/transformation/transformers/spec/block-scoped-functions.js
@@ -23,6 +23,16 @@ function statementList(key, path, file) {
   }
 }
 
+export function shouldVisit(node) {
+  if (node.type !== "BlockStatement") return false;
+
+  for (var i = 0; i < node.body.length; i++) {
+    if (node.body[i].type === "FunctionDeclaration") return true;
+  }
+
+  return false;
+}
+
 export function BlockStatement(node, parent, scope, file) {
   if ((t.isFunction(parent) && parent.body === node) || t.isExportDeclaration(parent)) {
     return;
diff --git a/src/babel/traversal/path/index.js b/src/babel/traversal/path/index.js
index 267dbbd507..b7d6ffc201 100644
--- a/src/babel/traversal/path/index.js
+++ b/src/babel/traversal/path/index.js
@@ -253,15 +253,32 @@ export default class TraversalPath {
   }
 
   remove() {
-    var removeParent = false;
-    if (this.parentPath) {
-      removeParent ||= this.parentPath.isExpressionStatement();
-      removeParent ||= this.parentPath.isSequenceExpression() && this.parent.expressions.length === 1;
-      if (removeParent) return this.parentPath.remove();
-    }
-
     this._remove();
     this.removed = true;
+
+    var parentPath = this.parentPath;
+    var parent = this.parent;
+    if (!parentPath) return;
+
+    // we're the child of an expression statement so we should remove the parent
+    if (parentPath.isExpressionStatement()) {
+      return parentPath.remove();
+    }
+
+    // we've just removed the second element of a sequence expression so let's turn that sequence
+    // expression into a regular expression
+    if (parentPath.isSequenceExpression() && parent.expressions.length === 1) {
+      parentPath.replaceWith(parent.expressions[0]);
+    }
+
+    // we're in a binary expression, better remove it and replace it with the last expression
+    if (parentPath.isBinary()) {
+      if (this.key === "left") {
+        parentPath.replaceWith(parent.right);
+      } else { // key === "right"
+        parentPath.replaceWith(parent.left);
+      }
+    }
   }
 
   skip() {
diff --git a/src/babel/types/index.js b/src/babel/types/index.js
index 312916c0fc..e731f40ade 100644
--- a/src/babel/types/index.js
+++ b/src/babel/types/index.js
@@ -78,7 +78,11 @@ export function isType(nodeType, targetType) {
   if (nodeType === targetType) return true;
 
   var aliases = t.FLIPPED_ALIAS_KEYS[targetType];
-  if (aliases) return aliases.indexOf(nodeType) > -1;
+  if (aliases) {
+    for (var i = 0; i < aliases.length; i++) {
+      if (nodeType === aliases[i]) return true;
+    }
+  }
 
   return false;
 }