var Bubble = Container.expand(function () {
	var self = Container.call(this);
	var bubbleGraphics = self.createAsset('bubble', 'Bubble Graphics', .5, .5);
	self.move = function () {};
	self.pop = function () {};
});
var Hero = Container.expand(function () {
	var self = Container.call(this);
	var heroGraphics = self.createAsset('hero', 'Hero Graphics', .5, .5);
	self.shoot = function () {};
	self.update = function () {};
});
var Enemy = Container.expand(function () {
	var self = Container.call(this);
	var enemyGraphics = self.createAsset('enemy', 'Enemy Graphics', .5, .5);
	self.move = function () {};
	self.attack = function () {};
});
var Game = Container.expand(function () {
	var self = Container.call(this);
	var bubbles = [];
	var enemies = [];
	var hero = self.addChild(new Hero());
	hero.x = 2048 / 2;
	hero.y = 2732 - hero.height;
	var spawnBubble = function () {
		var newBubble = new Bubble();
		bubbles.push(newBubble);
		self.addChild(newBubble);
	};
	var spawnEnemy = function () {
		var newEnemy = new Enemy();
		enemies.push(newEnemy);
		self.addChild(newEnemy);
	};
	LK.on('tick', function () {
		hero.update();
		for (var i = 0; i < bubbles.length; i++) {
			bubbles[i].move();
		}
		for (var i = 0; i < enemies.length; i++) {
			enemies[i].move();
		}
		if (LK.ticks % 60 == 0) {
			spawnBubble();
		}
		if (LK.ticks % 300 == 0) {
			spawnEnemy();
		}
	});
});

===================================================================
--- original.js
+++ change.js
@@ -7,8 +7,9 @@
 var Hero = Container.expand(function () {
 	var self = Container.call(this);
 	var heroGraphics = self.createAsset('hero', 'Hero Graphics', .5, .5);
 	self.shoot = function () {};
+	self.update = function () {};
 });
 var Enemy = Container.expand(function () {
 	var self = Container.call(this);
 	var enemyGraphics = self.createAsset('enemy', 'Enemy Graphics', .5, .5);