diff --git a/lib/legacy/class.js b/lib/legacy/class.js
index 65ca95b1e8..e1717f6d8a 100644
--- a/lib/legacy/class.js
+++ b/lib/legacy/class.js
@@ -11,7 +11,7 @@ subject to an additional IP rights grant found at http://polymer.github.io/PATEN
 import { LegacyElementMixin } from './legacy-element-mixin.js';
 import { DomModule } from '../elements/dom-module.js';
 
-let metaProps = {
+const metaProps = {
   attached: true,
   detached: true,
   ready: true,
@@ -19,15 +19,22 @@ let metaProps = {
   beforeRegister: true,
   registered: true,
   attributeChanged: true,
-  // meta objects
-  behaviors: true
 };
 
+const noBehaviorCopyProps = Object.assign({
+  behaviors: true
+}, metaProps);
+
+const memoizedProps = Object.assign({
+  listeners: true,
+  hostAttributes: true
+}, metaProps);
+
 function copyProperties(source, target) {
   for (let p in source) {
-    // NOTE: cannot copy `metaProps` methods onto prototype at least because
+    // NOTE: cannot copy `noBehaviorCopyProps` methods onto prototype at least because
     // `super.ready` must be called and is not included in the user fn.
-    if (!(p in metaProps)) {
+    if (!(p in noBehaviorCopyProps)) {
       let pd = Object.getOwnPropertyDescriptor(source, p);
       if (pd) {
         Object.defineProperty(target, p, pd);
@@ -36,7 +43,6 @@ function copyProperties(source, target) {
   }
 }
 
-// TODO(sorvell): this breaks `Polymer.mixinBehaviors`; should fix via factoring
 /**
  * Applies a "legacy" behavior or array of behaviors to the provided class.
  *
@@ -53,37 +59,7 @@ function copyProperties(source, target) {
  * @suppress {invalidCasts, checkTypes}
  */
 export function mixinBehaviors(behaviors, klass) {
-  if (behaviors) {
-    klass = applyBehaviors(behaviors, klass);
-  }
-  // provides behaviors functionality
-  return GenerateClassFromInfo({}, klass);
-}
-
-
-function applyBehaviors(behaviors, klass) {
-  if (!behaviors) {
-    klass = /** @type {HTMLElement} */(klass); // eslint-disable-line no-self-assign
-    return klass;
-  }
-  // NOTE: ensure the behavior is extending a class with
-  // legacy element api. This is necessary since behaviors expect to be able
-  // to access 1.x legacy api.
-  klass = class extends LegacyElementMixin(klass) {};
-  if (!Array.isArray(behaviors)) {
-    behaviors = [behaviors];
-  }
-  let superBehaviors = klass.prototype.behaviors;
-  // get flattened, deduped list of behaviors *not* already on super class
-  behaviors = flattenBehaviors(behaviors, null, superBehaviors);
-  // mixin new behaviors
-  klass = _applyBehaviors(behaviors, klass);
-  if (superBehaviors) {
-    behaviors = superBehaviors.concat(behaviors);
-  }
-  // Set behaviors on prototype for BC...
-  klass.prototype.behaviors = behaviors;
-  return klass;
+  return GenerateClassFromInfo({}, LegacyElementMixin(klass), behaviors);
 }
 
 // NOTE:
@@ -116,15 +92,26 @@ function applyBehaviors(behaviors, klass) {
 // If lifecycle is called (super then me), order is
 // (1) C.created, (2) A.created, (3) B.created, (4) element.created
 // (again same as 1.x)
-function _applyBehaviors(behaviors, klass) {
-  for (let i=0; i<behaviors.length; i++) {
-    let b = behaviors[i];
-    if (b) {
-      Array.isArray(b) ? _applyBehaviors(b, klass) :
-        copyProperties(b, klass.prototype);
+function copyBehaviorProperties(behaviors, klass) {
+  const meta = {};
+  const superMeta = klass.prototype.__behaviorMetaProps;
+  if (behaviors) {
+    klass.prototype.__behaviorMetaProps = meta;
+    for (let i=0; i<behaviors.length; i++) {
+      copyProperties(behaviors[i], klass.prototype);
+      memoizeBehaviorMetaProps(meta, behaviors[i], superMeta);
+    }
+  }
+  klass.prototype.__behaviorMetaProps = meta;
+}
+
+function memoizeBehaviorMetaProps(meta, behavior, superMeta) {
+  for (let p in memoizedProps) {
+    if (behavior[p]) {
+      meta[p] = meta[p] || (superMeta && superMeta[p] ? superMeta[p].slice() : []);
+      meta[p].push(behavior[p]);
     }
   }
-  return klass;
 }
 
 /**
@@ -202,20 +189,20 @@ function mergeProperties(a, b) {
 /**
  * @param {!PolymerInit} info Polymer info object
  * @param {function(new:HTMLElement)} Base base class to extend with info object
+ * @param {Object} behaviors behaviors to copy into the element
  * @return {function(new:HTMLElement)} Generated class
  * @suppress {checkTypes}
  * @private
  */
-function GenerateClassFromInfo(info, Base) {
+function GenerateClassFromInfo(info, Base, behaviors) {
 
   /** @private */
   class PolymerGenerated extends Base {
-
     static get properties() {
       const properties = {};
-      if (this.prototype.behaviors) {
-        for (let i=0, b; i < this.prototype.behaviors.length; i++) {
-          b = this.prototype.behaviors[i];
+      if (this.prototype.__behaviors) {
+        for (let i=0, b; i < this.prototype.__behaviors.length; i++) {
+          b = this.prototype.__behaviors[i];
           mergeProperties(properties, b.properties);
         }
       }
@@ -225,9 +212,9 @@ function GenerateClassFromInfo(info, Base) {
 
     static get observers() {
       let observers = [];
-      if (this.prototype.behaviors) {
-        for (let i=0, b; i < this.prototype.behaviors.length; i++) {
-          b = this.prototype.behaviors[i];
+      if (this.prototype.__behaviors) {
+        for (let i=0, b; i < this.prototype.__behaviors.length; i++) {
+          b = this.prototype.__behaviors[i];
           if (b.observers) {
             observers = observers.concat(b.observers);
           }
@@ -243,12 +230,10 @@ function GenerateClassFromInfo(info, Base) {
      * @return {void}
      */
     created() {
-      if (this.behaviors) {
-        for (let i=0, b; i < this.behaviors.length; i++) {
-          b = this.behaviors[i];
-          if (b.created) {
-            b.created.call(this);
-          }
+      const list = this.__behaviorMetaProps.created;
+      if (list) {
+        for (let i=0; i < list.length; i++) {
+          list[i].call(this);
         }
       }
       if (info.created) {
@@ -259,30 +244,39 @@ function GenerateClassFromInfo(info, Base) {
     /**
      * @return {void}
      */
+    // Called on element prototype
     _registered() {
       /* NOTE: `beforeRegister` is called here for bc, but the behavior
-       is different than in 1.x. In 1.0, the method was called *after*
-       mixing prototypes together but *before* processing of meta-objects.
-       However, dynamic effects can still be set here and can be done either
-       in `beforeRegister` or `registered`. It is no longer possible to set
-       `is` in `beforeRegister` as you could in 1.x.
+        is different than in 1.x. In 1.0, the method was called *after*
+        mixing prototypes together but *before* processing of meta-objects.
+        However, dynamic effects can still be set here and can be done either
+        in `beforeRegister` or `registered`. It is no longer possible to set
+        `is` in `beforeRegister` as you could in 1.x.
       */
-      if (this.behaviors) {
-        for (let i=0, b; i < this.behaviors.length; i++) {
-          b = this.behaviors[i];
-          if (b.beforeRegister) {
-            b.beforeRegister.call(Object.getPrototypeOf(this));
-          }
-          if (b.registered) {
-            b.registered.call(Object.getPrototypeOf(this));
-          }
+      const proto = this;
+      if (proto.hasOwnProperty('__behaviors')) {
+        copyBehaviorProperties(proto.__behaviors, proto.constructor);
+      }
+      proto.__behaviorMetaProps = proto.__behaviorMetaProps || {};
+      copyProperties(info, proto);
+      // Note, previously these were interleaved.
+      let list = proto.__behaviorMetaProps.beforeRegister;
+      if (list) {
+        for (let i=0; i < list.length; i++) {
+          list[i].call(proto);
+        }
+      }
+      list = proto.__behaviorMetaProps.registered;
+      if (list) {
+        for (let i=0; i < list.length; i++) {
+          list[i].call(proto);
         }
       }
       if (info.beforeRegister) {
-        info.beforeRegister.call(Object.getPrototypeOf(this));
+        info.beforeRegister.call(proto);
       }
       if (info.registered) {
-        info.registered.call(Object.getPrototypeOf(this));
+        info.registered.call(proto);
       }
     }
 
@@ -290,12 +284,13 @@ function GenerateClassFromInfo(info, Base) {
      * @return {void}
      */
     _applyListeners() {
-      if (this.behaviors) {
-        for (let i=0, b; i < this.behaviors.length; i++) {
-          b = this.behaviors[i];
-          if (b.listeners) {
-            for (let l in b.listeners) {
-              this._addMethodEventListenerToNode(this, l, b.listeners[l]);
+      const list = this.__behaviorMetaProps.listeners;
+      if (list) {
+        for (let i=0; i < list.length; i++) {
+          const listeners = list[i];
+          if (listeners) {
+            for (let l in listeners) {
+              this._addMethodEventListenerToNode(this, l, listeners[l]);
             }
           }
         }
@@ -319,14 +314,13 @@ function GenerateClassFromInfo(info, Base) {
           this._ensureAttribute(a, info.hostAttributes[a]);
         }
       }
-      if (this.behaviors) {
-        for (let i=this.behaviors.length-1, b; i >= 0; i--) {
-          b = this.behaviors[i];
-          if (b.hostAttributes) {
-            for (let a in b.hostAttributes) {
-              this._ensureAttribute(a, b.hostAttributes[a]);
+      const list = this.__behaviorMetaProps.hostAttributes;
+      if (list) {
+        for (let i=list.length-1; i >= 0; i--) {
+          const hostAttributes = list[i];
+          for (let a in hostAttributes) {
+              this._ensureAttribute(a, hostAttributes[a]);
             }
-          }
         }
       }
     }
@@ -336,12 +330,10 @@ function GenerateClassFromInfo(info, Base) {
      */
     ready() {
       super.ready();
-      if (this.behaviors) {
-        for (let i=0, b; i < this.behaviors.length; i++) {
-          b = this.behaviors[i];
-          if (b.ready) {
-            b.ready.call(this);
-          }
+      let list = this.__behaviorMetaProps.ready;
+      if (list) {
+        for (let i=0; i < list.length; i++) {
+          list[i].call(this);
         }
       }
       if (info.ready) {
@@ -353,12 +345,10 @@ function GenerateClassFromInfo(info, Base) {
      * @return {void}
      */
     attached() {
-      if (this.behaviors) {
-        for (let i=0, b; i < this.behaviors.length; i++) {
-          b = this.behaviors[i];
-          if (b.attached) {
-            b.attached.call(this);
-          }
+      let list = this.__behaviorMetaProps.attached;
+      if (list) {
+        for (let i=0; i < list.length; i++) {
+          list[i].call(this);
         }
       }
       if (info.attached) {
@@ -370,12 +360,10 @@ function GenerateClassFromInfo(info, Base) {
      * @return {void}
      */
     detached() {
-      if (this.behaviors) {
-        for (let i=0, b; i < this.behaviors.length; i++) {
-          b = this.behaviors[i];
-          if (b.detached) {
-            b.detached.call(this);
-          }
+      let list = this.__behaviorMetaProps.detached;
+      if (list) {
+        for (let i=0; i < list.length; i++) {
+          list[i].call(this);
         }
       }
       if (info.detached) {
@@ -384,6 +372,7 @@ function GenerateClassFromInfo(info, Base) {
     }
 
     /**
+     *
      * Implements native Custom Elements `attributeChangedCallback` to
      * set an attribute value to a property via `_attributeToProperty`.
      *
@@ -393,23 +382,36 @@ function GenerateClassFromInfo(info, Base) {
      * @return {void}
      */
     attributeChanged(name, old, value) {
-      if (this.behaviors) {
-        for (let i=0, b; i < this.behaviors.length; i++) {
-          b = this.behaviors[i];
-          if (b.attributeChanged) {
-            b.attributeChanged.call(this, name, old, value);
-          }
+      let list = this.__behaviorMetaProps.attributeChanged;
+      if (list) {
+        for (let i=0; i < list.length; i++) {
+          list[i].call(this, name, old, value);
         }
       }
       if (info.attributeChanged) {
         info.attributeChanged.call(this, name, old, value);
       }
-   }
+    }
+
   }
 
-  PolymerGenerated.generatedFrom = info;
+  // apply behaviors
+  if (behaviors) {
+    // NOTE: ensure the behavior is extending a class with
+    // legacy element api. This is necessary since behaviors expect to be able
+    // to access 1.x legacy api.
+    if (!Array.isArray(behaviors)) {
+      behaviors = [behaviors];
+    }
+    let superBehaviors = PolymerGenerated.prototype.behaviors;
+    // get flattened, deduped list of behaviors *not* already on super class
+    behaviors = flattenBehaviors(behaviors, null, superBehaviors);
+    PolymerGenerated.prototype.behaviors = superBehaviors ?
+      superBehaviors.concat(behaviors) : behaviors;
+    PolymerGenerated.prototype.__behaviors = behaviors;
+  }
 
-  copyProperties(info, PolymerGenerated.prototype);
+  PolymerGenerated.generatedFrom = info;
 
   return PolymerGenerated;
 }
@@ -486,14 +488,11 @@ function GenerateClassFromInfo(info, Base) {
  */
 export const Class = function(info, mixin) {
   if (!info) {
-    console.warn(`Polymer's Class function requires \`info\` argument`);
+    console.warn('Polymer.Class requires `info` argument');
   }
   let klass = mixin ? mixin(LegacyElementMixin(HTMLElement)) :
       LegacyElementMixin(HTMLElement);
-  if (info.behaviors) {
-    klass = applyBehaviors(info.behaviors, klass);
-  }
-  klass = GenerateClassFromInfo(info, klass);
+  klass = GenerateClassFromInfo(info, klass, info.behaviors);
   // decorate klass with registration info
   klass.is = info.is;
   return klass;
diff --git a/lib/legacy/legacy-element-mixin.js b/lib/legacy/legacy-element-mixin.js
index a6d00c1671..d3ffdcba7e 100644
--- a/lib/legacy/legacy-element-mixin.js
+++ b/lib/legacy/legacy-element-mixin.js
@@ -77,11 +77,6 @@ export const LegacyElementMixin = dedupingMixin((base) => {
       this.__boundListeners;
       /** @type {Object<string, Function>} */
       this._debouncers;
-      // Ensure listeners are applied immediately so that they are
-      // added before declarative event listeners. This allows an element to
-      // decorate itself via an event prior to any declarative listeners
-      // seeing the event. Note, this ensures compatibility with 1.x ordering.
-      this._applyListeners();
     }
 
     /**
@@ -96,6 +91,11 @@ export const LegacyElementMixin = dedupingMixin((base) => {
       return this.prototype.importMeta;
     }
 
+    static _finalizeClass() {
+      this.prototype._registered();
+      super._finalizeClass();
+    }
+
     /**
      * Legacy callback called during the `constructor`, for overriding
      * by the user.
@@ -178,14 +178,14 @@ export const LegacyElementMixin = dedupingMixin((base) => {
      * @suppress {invalidCasts}
      */
     _initializeProperties() {
-      let proto = Object.getPrototypeOf(this);
-      if (!proto.hasOwnProperty('__hasRegisterFinished')) {
-        proto.__hasRegisterFinished = true;
-        this._registered();
-      }
       super._initializeProperties();
       this.root = /** @type {HTMLElement} */(this);
       this.created();
+      // Ensure listeners are applied immediately so that they are
+      // added before declarative event listeners. This allows an element to
+      // decorate itself via an event prior to any declarative listeners
+      // seeing the event. Note, this ensures compatibility with 1.x ordering.
+      this._applyListeners();
     }
 
     /**
diff --git a/lib/mixins/element-mixin.js b/lib/mixins/element-mixin.js
index 8cca1a2bfd..35bbb6432b 100644
--- a/lib/mixins/element-mixin.js
+++ b/lib/mixins/element-mixin.js
@@ -16,7 +16,7 @@ import { pathFromUrl, resolveCss, resolveUrl } from '../utils/resolve-url.js';
 import { DomModule } from '../elements/dom-module.js';
 import { PropertyEffects } from './property-effects.js';
 import { PropertiesMixin } from './properties-mixin.js';
-import { skipStyleIncludesAndUrls } from '../utils/settings.js';
+import { legacyOptimizations } from '../utils/settings.js';
 
 /**
  * Current Polymer version in Semver notation.
@@ -24,6 +24,8 @@ import { skipStyleIncludesAndUrls } from '../utils/settings.js';
  */
 export const version = '3.0.5';
 
+const builtCSS = window.ShadyCSS && window.ShadyCSS['cssBuild'];
+
 /**
  * Element class mixin that provides the core API for Polymer's meta-programming
  * features including template stamping, data-binding, attribute deserialization,
@@ -253,7 +255,7 @@ export const ElementMixin = dedupingMixin(base => {
    * @private
    */
   function processElementStyles(klass, template, is, baseURI) {
-    if (!skipStyleIncludesAndUrls) {
+    if (!builtCSS) {
       const templateStyles = template.content.querySelectorAll('style');
       const stylesWithImports = stylesFromTemplate(template);
       // insert styles from <link rel="import" type="css"> at the top of the template
@@ -335,10 +337,6 @@ export const ElementMixin = dedupingMixin(base => {
      */
    static _finalizeClass() {
       super._finalizeClass();
-      if (this.hasOwnProperty(
-        JSCompiler_renameProperty('is', this)) &&  this.is) {
-        register(this.prototype);
-      }
       const observers = ownObservers(this);
       if (observers) {
         this.createObservers(observers, this._properties);
@@ -349,7 +347,7 @@ export const ElementMixin = dedupingMixin(base => {
         if (typeof template === 'string') {
           console.error('template getter must return HTMLTemplateElement');
           template = null;
-        } else {
+        } else if (!legacyOptimizations) {
           template = template.cloneNode(true);
         }
       }
@@ -524,7 +522,6 @@ export const ElementMixin = dedupingMixin(base => {
      * @suppress {invalidCasts}
      */
     _initializeProperties() {
-      instanceCount++;
       this.constructor.finalize();
       // note: finalize template when we have access to `localName` to
       // avoid dependence on `is` for polyfilling styling.
@@ -743,46 +740,6 @@ export const ElementMixin = dedupingMixin(base => {
   return PolymerElement;
 });
 
-/**
- * Total number of Polymer element instances created.
- * @type {number}
- */
-export let instanceCount = 0;
-
-/**
- * Array of Polymer element classes that have been finalized.
- * @type {Array<PolymerElement>}
- */
-export const registrations = [];
-
-/**
- * @param {!PolymerElementConstructor} prototype Element prototype to log
- * @this {this}
- * @private
- */
-function _regLog(prototype) {
-  console.log('[' + prototype.is + ']: registered');
-}
-
-/**
- * Registers a class prototype for telemetry purposes.
- * @param {HTMLElement} prototype Element prototype to register
- * @this {this}
- * @protected
- */
-export function register(prototype) {
-  registrations.push(prototype);
-}
-
-/**
- * Logs all elements registered with an `is` to the console.
- * @public
- * @this {this}
- */
-export function dumpRegistrations() {
-  registrations.forEach(_regLog);
-}
-
 /**
  * When using the ShadyCSS scoping and custom property shim, causes all
  * shimmed `styles` (via `custom-style`) in the document (and its subtree)
diff --git a/lib/mixins/properties-mixin.js b/lib/mixins/properties-mixin.js
index e9f558424b..871937bac2 100644
--- a/lib/mixins/properties-mixin.js
+++ b/lib/mixins/properties-mixin.js
@@ -10,6 +10,7 @@ subject to an additional IP rights grant found at http://polymer.github.io/PATEN
 import '../utils/boot.js';
 
 import { dedupingMixin } from '../utils/mixin.js';
+import { register, incrementInstanceCount } from '../utils/telemetry.js';
 import { PropertiesChanged } from './properties-changed.js';
 
 /**
@@ -114,8 +115,12 @@ export const PropertiesMixin = dedupingMixin(superClass => {
     * @suppress {missingProperties} Interfaces in closure do not inherit statics, but classes do
     */
    static get observedAttributes() {
-     const props = this._properties;
-     return props ? Object.keys(props).map(p => this.attributeNameForProperty(p)) : [];
+     if (!this.hasOwnProperty('__observedAttributes')) {
+       register(this.prototype);
+       const props = this._properties;
+       this.__observedAttributes = props ? Object.keys(props).map(p => this.attributeNameForProperty(p)) : [];
+     }
+     return this.__observedAttributes;
    }
 
    /**
@@ -189,6 +194,7 @@ export const PropertiesMixin = dedupingMixin(superClass => {
     * @return {void}
     */
    _initializeProperties() {
+     incrementInstanceCount();
      this.constructor.finalize();
      super._initializeProperties();
    }
diff --git a/lib/mixins/template-stamp.js b/lib/mixins/template-stamp.js
index 3ae0607e01..0a36157c92 100644
--- a/lib/mixins/template-stamp.js
+++ b/lib/mixins/template-stamp.js
@@ -10,6 +10,9 @@ subject to an additional IP rights grant found at http://polymer.github.io/PATEN
 import '../utils/boot.js';
 
 import { dedupingMixin } from '../utils/mixin.js';
+import { legacyOptimizations } from '../utils/settings.js';
+
+const walker = document.createTreeWalker(document);
 
 // 1.x backwards-compatible auto-wrapper for template type extensions
 // This is a clear layering violation and gives favored-nation status to
@@ -45,7 +48,8 @@ function findTemplateNode(root, nodeInfo) {
   if (parent) {
     // note: marginally faster than indexing via childNodes
     // (http://jsperf.com/childnodes-lookup)
-    for (let n=parent.firstChild, i=0; n; n=n.nextSibling) {
+    walker.currentNode = parent;
+    for (let n=walker.firstChild(), i=0; n; n=walker.nextSibling()) {
       if (nodeInfo.parentIndex === i++) {
         return n;
       }
@@ -200,7 +204,7 @@ export const TemplateStamp = dedupingMixin(
       if (!template._templateInfo) {
         let templateInfo = template._templateInfo = {};
         templateInfo.nodeInfoList = [];
-        templateInfo.stripWhiteSpace =
+        templateInfo.stripWhiteSpace = legacyOptimizations ||
           (outerTemplateInfo && outerTemplateInfo.stripWhiteSpace) ||
           template.hasAttribute('strip-whitespace');
         this._parseTemplateContent(template, templateInfo, {parent: null});
@@ -234,7 +238,8 @@ export const TemplateStamp = dedupingMixin(
         // For ShadyDom optimization, indicating there is an insertion point
         templateInfo.hasInsertionPoint = true;
       }
-      if (element.firstChild) {
+      walker.currentNode = element;
+      if (walker.firstChild()) {
         noted = this._parseTemplateChildNodes(element, templateInfo, nodeInfo) || noted;
       }
       if (element.hasAttributes && element.hasAttributes()) {
@@ -260,7 +265,8 @@ export const TemplateStamp = dedupingMixin(
       if (root.localName === 'script' || root.localName === 'style') {
         return;
       }
-      for (let node=root.firstChild, parentIndex=0, next; node; node=next) {
+      walker.currentNode = root;
+      for (let node=walker.firstChild(), parentIndex=0, next; node; node=next) {
         // Wrap templates
         if (node.localName == 'template') {
           node = wrapTemplateExtension(node);
@@ -269,12 +275,13 @@ export const TemplateStamp = dedupingMixin(
         // text nodes to be inexplicably split =(
         // note that root.normalize() should work but does not so we do this
         // manually.
-        next = node.nextSibling;
+        walker.currentNode = node;
+        next = walker.nextSibling();
         if (node.nodeType === Node.TEXT_NODE) {
           let /** Node */ n = next;
           while (n && (n.nodeType === Node.TEXT_NODE)) {
             node.textContent += n.textContent;
-            next = n.nextSibling;
+            next = walker.nextSibling();
             root.removeChild(n);
             n = next;
           }
@@ -289,7 +296,8 @@ export const TemplateStamp = dedupingMixin(
           childInfo.infoIndex = templateInfo.nodeInfoList.push(/** @type {!NodeInfo} */(childInfo)) - 1;
         }
         // Increment if not removed
-        if (node.parentNode) {
+        walker.currentNode = node;
+        if (walker.parentNode()) {
           parentIndex++;
         }
       }
diff --git a/lib/utils/settings.js b/lib/utils/settings.js
index 5f4c0e443c..cdbcb8e36c 100644
--- a/lib/utils/settings.js
+++ b/lib/utils/settings.js
@@ -128,15 +128,16 @@ export const setAllowTemplateFromDomModule = function(allowDomModule) {
  * If no includes or relative urls are used in styles, these steps can be
  * skipped as an optimization.
  */
-export let skipStyleIncludesAndUrls = false;
+export let legacyOptimizations = false;
 
 /**
- * Sets `setSkipRewriteStyleUrls` globally for all elements
+ * Sets `legacyOptimizations` globally for all elements to enable optimizations
+ * when only legacy based elements are used.
  *
- * @param {boolean} skipIncludesAndUrls enable or disable skipping style
+ * @param {boolean} useLegacyOptimizations enable or disable legacy optimizations
  * includes and url rewriting
  * @return {void}
  */
-export const setSkipStyleIncludesAndUrls = function(skipIncludesAndUrls) {
-  skipStyleIncludesAndUrls = skipIncludesAndUrls;
+export const setLegacyOptimizations = function(useLegacyOptimizations) {
+  legacyOptimizations = useLegacyOptimizations;
 };
\ No newline at end of file
diff --git a/lib/utils/telemetry.js b/lib/utils/telemetry.js
new file mode 100644
index 0000000000..6668ac5271
--- /dev/null
+++ b/lib/utils/telemetry.js
@@ -0,0 +1,53 @@
+/**
+@license
+Copyright (c) 2017 The Polymer Project Authors. All rights reserved.
+This code may only be used under the BSD style license found at http://polymer.github.io/LICENSE.txt
+The complete set of authors may be found at http://polymer.github.io/AUTHORS.txt
+The complete set of contributors may be found at http://polymer.github.io/CONTRIBUTORS.txt
+Code distributed by Google as part of the polymer project is also
+subject to an additional IP rights grant found at http://polymer.github.io/PATENTS.txt
+*/
+
+/**
+ * Total number of Polymer element instances created.
+ * @type {number}
+ */
+export let instanceCount = 0;
+
+export function incrementInstanceCount() {
+  instanceCount++;
+}
+
+/**
+ * Array of Polymer element classes that have been finalized.
+ * @type {Array<PolymerElement>}
+ */
+export const registrations = [];
+
+/**
+ * @param {!PolymerElementConstructor} prototype Element prototype to log
+ * @this {this}
+ * @private
+ */
+function _regLog(prototype) {
+  console.log('[' + prototype.is + ']: registered');
+}
+
+/**
+ * Registers a class prototype for telemetry purposes.
+ * @param {HTMLElement} prototype Element prototype to register
+ * @this {this}
+ * @protected
+ */
+export function register(prototype) {
+  registrations.push(prototype);
+}
+
+/**
+ * Logs all elements registered with an `is` to the console.
+ * @public
+ * @this {this}
+ */
+export function dumpRegistrations() {
+  registrations.forEach(_regLog);
+}
diff --git a/test/unit/disable-upgrade.html b/test/unit/disable-upgrade.html
index 14dae2b60d..1c1fc78d7e 100644
--- a/test/unit/disable-upgrade.html
+++ b/test/unit/disable-upgrade.html
@@ -93,13 +93,17 @@ <h2 id="element">[[prop]]</h2>
       type: String
     }
   },
+  listeners: {
+    foo: 'fooHandler'
+  },
   created() {
     this.hasCreated = true;
     this.prop = 'enabled!';
   },
   ready() {
     this.enabled = true;
-  }
+  },
+  fooHandler() {}
 });
 
 Polymer({
@@ -241,30 +245,39 @@ <h2 id="element">[[prop]]</h2>
     assert.ok(el.$.enabledEl.enabled);
     assert.ok(el.$.enabledEl.$.element);
     assert.equal(el.$.enabledEl.$.element.textContent, 'enabled!');
+    el.$.enabledEl.fooHandler = sinon.spy();
+    el.$.enabledEl.fire('foo');
+    assert.equal(el.$.enabledEl.fooHandler.callCount, 1);
     assert.notOk(el.$.disabledEl.hasCreated);
     assert.notOk(el.$.disabledEl.enabled);
     assert.notOk(el.$.disabledEl.$);
+    el.$.disabledEl.fooHandler = sinon.spy();
+    el.$.disabledEl.fire('foo');
+    assert.equal(el.$.disabledEl.fooHandler.callCount, 0);
     assert.notOk(el.$.disabledBoundEl.hasCreated);
     assert.notOk(el.$.disabledBoundEl.enabled);
     assert.notOk(el.$.disabledBoundEl.$);
+    el.$.disabledBoundEl.fooHandler = sinon.spy();
+    el.$.disabledBoundEl.fire('foo');
+    assert.equal(el.$.disabledBoundEl.fooHandler.callCount, 0);
   });
 
   test('elements upgrade when `disable-upgrade` removed', function() {
-    assert.notOk(el.$.disabledEl.hasCreated);
-    assert.notOk(el.$.disabledEl.enabled);
-    assert.notOk(el.$.disabledEl.$);
-    assert.notOk(el.$.disabledBoundEl.hasCreated);
-    assert.notOk(el.$.disabledBoundEl.enabled);
-    assert.notOk(el.$.disabledBoundEl.$);
     el.enable();
     assert.ok(el.$.disabledEl.hasCreated);
     assert.ok(el.$.disabledEl.enabled);
     assert.ok(el.$.disabledEl.$.element);
     assert.equal(el.$.disabledEl.$.element.textContent, 'enabled!');
+    el.$.disabledEl.fooHandler = sinon.spy();
+    el.$.disabledEl.fire('foo');
+    assert.equal(el.$.disabledEl.fooHandler.callCount, 1);
     assert.ok(el.$.disabledBoundEl.hasCreated);
     assert.ok(el.$.disabledBoundEl.enabled);
     assert.ok(el.$.disabledBoundEl.$.element);
     assert.equal(el.$.disabledBoundEl.$.element.textContent, 'enabled!');
+    el.$.disabledBoundEl.fooHandler = sinon.spy();
+    el.$.disabledBoundEl.fire('foo');
+    assert.equal(el.$.disabledBoundEl.fooHandler.callCount, 1);
   });
 
 
diff --git a/test/unit/mixin-behaviors.html b/test/unit/mixin-behaviors.html
index 7c16962b20..8de238d2d0 100644
--- a/test/unit/mixin-behaviors.html
+++ b/test/unit/mixin-behaviors.html
@@ -256,12 +256,12 @@
 import { mixinBehaviors } from '../../lib/legacy/class.js';
 import { PolymerElement } from '../../polymer-element.js';
 customElements.define('nested-behaviors',
-  class extends mixinBehaviors(
-    [
-      [window.BehaviorB, [window.BehaviorC, window.BehaviorB], window.BehaviorA],
-      [window.BehaviorD]
-    ], PolymerElement) {
-});
+  class extends mixinBehaviors([window.BehaviorD, window.LifeCycleBehavior1], mixinBehaviors(
+      [
+        [window.BehaviorB, [window.BehaviorC, window.BehaviorB], window.BehaviorA, window.LifeCycleBehavior2],
+      ], PolymerElement)) {
+  }
+);
 </script>
   </dom-module>
 
@@ -355,7 +355,7 @@
 
   <test-fixture id="nested">
     <template>
-      <nested-behaviors></nested-behaviors>
+      <nested-behaviors foo="foo"></nested-behaviors>
     </template>
   </test-fixture>
 
@@ -554,7 +554,13 @@
   });
 
   test('nested-behavior dedups', function() {
-    assert.equal(el.behaviors.length, 4);
+    assert.equal(el.behaviors.length, 6);
+  });
+
+  test('nested-behavior lifecycle', function() {
+    assert.equal(el._calledCreated, 2, 'created call count wrong');
+    assert.equal(el._calledAttached, 2, 'attached call count wrong');
+    assert.equal(el._calledAttributeChanged, 1,  'attributeChanged call count wrong');
   });
 
   test('nested-behavior overrides ordering', function() {