/**** 
* Plugins
****/ 
var tween = LK.import("@upit/tween.v1");

/**** 
* Classes
****/ 
var Enemy = Container.expand(function () {
	var self = Container.call(this);
	var enemyGraphics = self.attachAsset('enemy', {
		anchorX: 0.5,
		anchorY: 0.5
	});
	self.speed = 3;
	self.direction = Math.random() < 0.5 ? -1 : 1;
	self.horizontalSpeed = Math.random() * 2 + 1;
	self.update = function () {
		self.y += self.speed;
		self.x += self.direction * self.horizontalSpeed;
		// Bounce off screen edges
		if (self.x < 30 || self.x > 2018) {
			self.direction *= -1;
		}
	};
	return self;
});
var Player = Container.expand(function () {
	var self = Container.call(this);
	var shipGraphics = self.attachAsset('playerShip', {
		anchorX: 0.5,
		anchorY: 0.5
	});
	return self;
});
var PlayerBullet = Container.expand(function () {
	var self = Container.call(this);
	var bulletGraphics = self.attachAsset('playerBullet', {
		anchorX: 0.5,
		anchorY: 0.5
	});
	self.speed = -12;
	self.update = function () {
		self.y += self.speed;
	};
	return self;
});

/**** 
* Initialize Game
****/ 
var game = new LK.Game({
	backgroundColor: 0x000033
});

/**** 
* Game Code
****/ 
var player = game.addChild(new Player());
player.x = 1024;
player.y = 2600;
var bullets = [];
var enemies = [];
var gameSpeed = 1;
var enemySpawnRate = 120;
var lastEnemySpawn = 0;
var scoreTxt = new Text2('0', {
	size: 80,
	fill: 0xFFFFFF
});
scoreTxt.anchor.set(0.5, 0);
LK.gui.top.addChild(scoreTxt);
scoreTxt.y = 50;
// Auto-fire bullets
var bulletTimer = LK.setInterval(function () {
	var newBullet = new PlayerBullet();
	newBullet.x = player.x;
	newBullet.y = player.y - 40;
	newBullet.lastY = newBullet.y;
	bullets.push(newBullet);
	game.addChild(newBullet);
	LK.getSound('shoot').play();
}, 150);
function handleMove(x, y, obj) {
	player.x = x;
	// Keep player within screen bounds
	if (player.x < 40) player.x = 40;
	if (player.x > 2008) player.x = 2008;
}
game.move = handleMove;
game.down = function (x, y, obj) {
	handleMove(x, y, obj);
};
// Start retro space music
LK.playMusic('retroSpaceMusic');
game.update = function () {
	// Spawn enemies
	if (LK.ticks - lastEnemySpawn > enemySpawnRate) {
		var newEnemy = new Enemy();
		newEnemy.x = Math.random() * (2048 - 120) + 60;
		newEnemy.y = -30;
		newEnemy.lastY = newEnemy.y;
		newEnemy.lastIntersecting = false;
		enemies.push(newEnemy);
		game.addChild(newEnemy);
		lastEnemySpawn = LK.ticks;
		// Increase difficulty over time
		if (enemySpawnRate > 40) {
			enemySpawnRate -= 0.5;
		}
	}
	// Update bullets
	for (var i = bullets.length - 1; i >= 0; i--) {
		var bullet = bullets[i];
		if (bullet.lastY === undefined) bullet.lastY = bullet.y;
		// Remove bullets that go off screen
		if (bullet.lastY >= -10 && bullet.y < -10) {
			bullet.destroy();
			bullets.splice(i, 1);
			continue;
		}
		// Check bullet-enemy collisions
		var bulletHit = false;
		for (var j = enemies.length - 1; j >= 0; j--) {
			var enemy = enemies[j];
			if (bullet.intersects(enemy)) {
				// Destroy both bullet and enemy
				LK.setScore(LK.getScore() + 10);
				scoreTxt.setText(LK.getScore());
				bullet.destroy();
				bullets.splice(i, 1);
				enemy.destroy();
				enemies.splice(j, 1);
				LK.getSound('enemyDestroy').play();
				bulletHit = true;
				break;
			}
		}
		if (!bulletHit) {
			bullet.lastY = bullet.y;
		}
	}
	// Update enemies
	for (var k = enemies.length - 1; k >= 0; k--) {
		var enemy = enemies[k];
		if (enemy.lastY === undefined) enemy.lastY = enemy.y;
		if (enemy.lastIntersecting === undefined) enemy.lastIntersecting = false;
		// Remove enemies that go off screen
		if (enemy.lastY <= 2732 && enemy.y > 2732) {
			enemy.destroy();
			enemies.splice(k, 1);
			continue;
		}
		// Check player-enemy collision
		var currentIntersecting = enemy.intersects(player);
		if (!enemy.lastIntersecting && currentIntersecting) {
			LK.getSound('playerHit').play();
			LK.effects.flashScreen(0xff0000, 1000);
			LK.showGameOver();
			return;
		}
		enemy.lastY = enemy.y;
		enemy.lastIntersecting = currentIntersecting;
	}
};

===================================================================
--- original.js
+++ change.js
@@ -90,8 +90,10 @@
 game.move = handleMove;
 game.down = function (x, y, obj) {
 	handleMove(x, y, obj);
 };
+// Start retro space music
+LK.playMusic('retroSpaceMusic');
 game.update = function () {
 	// Spawn enemies
 	if (LK.ticks - lastEnemySpawn > enemySpawnRate) {
 		var newEnemy = new Enemy();