var FastEnemy = Enemy.expand(function () {
	var self = Enemy.call(this) || this;
	self.speed = (5 + Math.random() * 10) * 2;
});
var HeroHealthItem = Container.expand(function () {
	var self = Container.call(this);
	var healthItemGraphics = self.createAsset('heroHealthItem', 'Hero Health Item Graphics', .5, .5);
	self.speed = -5;
	self.move = function () {
		self.y += self.speed;
		if (self.y < 0) {
			self.destroy();
		}
	};
});
var HeroBullet = Container.expand(function () {
	var self = Container.call(this);
	var bulletGraphics = self.createAsset('heroBullet', 'Hero Bullet Graphics', .5, .5);
	self.speed = 10;
	self.move = function () {
		self.x += self.speed;
		if (self.x > 2048) {
			self.destroy();
		}
	};
});
var EnemyBullet = Container.expand(function () {
	var self = Container.call(this);
	var bulletGraphics = self.createAsset('enemyBullet', 'Enemy Bullet Graphics', .5, .5);
	self.speed = -10;
	self.move = function () {
		self.x += self.speed;
	};
});
var Hero = Container.expand(function () {
	var self = Container.call(this);
	var heroGraphics = self.createAsset('hero', 'Hero Graphics', .5, .5);
	self.hitPoints = 5;
	self.hitPointIcons = [];
	self.takeDamage = function () {
		self.hitPoints--;
		if (self.hitPoints >= 0) {
			self.hitPointIcons[self.hitPoints].destroy();
			self.hitPointIcons.splice(self.hitPoints, 1);
		}
		if (self.hitPoints <= 0) {
			LK.showGameOver();
		}
	};
});
var Enemy = Container.expand(function () {
	var self = Container.call(this);
	var enemyGraphics = self.createAsset('enemy', 'Enemy Graphics', .5, .5);
	self.speed = 5 + Math.random() * 10;
	self.direction = 1;
	self.hitPoints = 3;
	self.move = function () {
		self.x -= self.speed;
		self.y += self.direction * 5;
		if (self.y > 2732 - self.height || self.y < self.height) {
			self.direction *= -1;
		}
	};
});
var Game = Container.expand(function () {
	var self = Container.call(this);
	var background = self.createAsset('background', 'Game Background', 0, 0);
	background.width = 2048;
	background.height = 2732;
	background.alpha = 0.5;
	var dragNode = null;
	var shootingInterval;
	stage.on('down', function (obj) {
		dragNode = hero;
		shootingInterval = LK.setInterval(function () {
			var bullet = new HeroBullet();
			bullet.x = hero.x;
			bullet.y = hero.y;
			heroBullets.push(bullet);
			self.addChild(bullet);
		}, 200);
	});
	stage.on('up', function (obj) {
		dragNode = null;
		LK.clearInterval(shootingInterval);
	});
	stage.on('move', function (obj) {
		if (dragNode) {
			var pos = obj.event.getLocalPosition(self);
			dragNode.x = pos.x;
			dragNode.y = pos.y;
		}
	});
	stage.on('up', function (obj) {
		dragNode = null;
	});
	var heroBullets = [];
	var enemyBullets = [];
	var enemies = [];
	var hero = self.addChild(new Hero());
	hero.x = hero.width;
	hero.y = 2732 / 2;
	var hitPointIcons = [];
	for (var i = 0; i < hero.hitPoints; i++) {
		var hitPointIcon = LK.getAsset('hpIcon', 'HP Icon', 0, 0);
		hitPointIcon.x = i * hitPointIcon.width;
		hitPointIcon.y = 0;
		hero.hitPointIcons.push(hitPointIcon);
		LK.gui.topLeft.addChild(hitPointIcon);
	}
	var score = 0;
	var scoreText = new Text2(score.toString(), {
		size: 150,
		fill: '#ffffff'
	});
	scoreText.anchor.set(1, 0);
	LK.gui.topRight.addChild(scoreText);
	LK.on('tick', function () {
		for (var i = 0; i < heroBullets.length; i++) {
			heroBullets[i].move();
			if (heroBullets[i].x > 2048) {
				heroBullets[i].destroy();
				heroBullets.splice(i, 1);
			}
			for (var j = 0; j < enemies.length; j++) {
				if (heroBullets[i] && heroBullets[i].intersects(enemies[j])) {
					enemies[j].hitPoints--;
					heroBullets[i].destroy();
					heroBullets.splice(i, 1);
					if (enemies[j].hitPoints <= 0) {
						var blast = self.createAsset('blast', 'Blast Graphics', .5, .5);
						blast.x = enemies[j].x;
						blast.y = enemies[j].y;
						self.addChild(blast);
						LK.setTimeout(function () {
							blast.destroy();
						}, 500);
						enemies[j].destroy();
						enemies.splice(j, 1);
						score++;
						scoreText.setText(score.toString());
					}
					break;
				}
			}
		}
		for (var i = 0; i < enemyBullets.length; i++) {
			enemyBullets[i].move();
			if (enemyBullets[i].x < 0) {
				enemyBullets[i].destroy();
				enemyBullets.splice(i, 1);
			}
		}
		for (var i = 0; i < enemies.length; i++) {
			enemies[i].move();
			if (enemies[i].x + enemies[i].width < 0) {
				enemies[i].destroy();
				enemies.splice(i, 1);
			}
			if (hero.intersects(enemies[i])) {
				hero.takeDamage();
				enemies[i].destroy();
				enemies.splice(i, 1);
			}
		}
		if (LK.ticks % 72 == 0) {
			var enemy;
			if (Math.random() < 0.3) {
				enemy = new FastEnemy();
			} else {
				enemy = new Enemy();
			}
			enemy.x = 2048;
			enemy.y = Math.random() * (2732 - 2 * enemy.height);
			enemies.push(enemy);
			self.addChild(enemy);
		}
		if (LK.ticks % 1200 == 0) {
			var healthItem = new HeroHealthItem();
			healthItem.x = Math.random() * (2048 - healthItem.width);
			healthItem.y = 2732;
			self.addChild(healthItem);
		}
		for (var i = 0; i < self.children.length; i++) {
			if (self.children[i] instanceof HeroHealthItem) {
				self.children[i].move();
				if (hero.intersects(self.children[i])) {
					if (hero.hitPoints < 5) {
						hero.hitPoints++;
						var hitPointIcon = LK.getAsset('hpIcon', 'HP Icon', 0, 0);
						hitPointIcon.x = (hero.hitPoints - 1) * hitPointIcon.width;
						hitPointIcon.y = 0;
						hero.hitPointIcons.push(hitPointIcon);
						LK.gui.topLeft.addChild(hitPointIcon);
					}
					self.children[i].destroy();
				}
			}
		}
	});
});

===================================================================
--- original.js
+++ change.js
@@ -1,6 +1,6 @@
 var FastEnemy = Enemy.expand(function () {
-	var self = Enemy.call(this);
+	var self = Enemy.call(this) || this;
 	self.speed = (5 + Math.random() * 10) * 2;
 });
 var HeroHealthItem = Container.expand(function () {
 	var self = Container.call(this);