var Hero = Container.expand(function () {
	var self = Container.call(this);
	var heroGraphics = self.createAsset('hero', 'Hero character', .5, .5);
	self.move = function () {};
	self.shoot = function () {};
});
var Enemy = Container.expand(function () {
	var self = Container.call(this);
	var enemyGraphics = self.createAsset('enemy', 'Enemy character', .5, .5);
	self.move = function () {};
});
var HeroBullet = Container.expand(function () {
	var self = Container.call(this);
	var bulletGraphics = self.createAsset('heroBullet', 'Hero Bullet', .5, .5);
	self.move = function () {};
});
var EnemyBullet = Container.expand(function () {
	var self = Container.call(this);
	var bulletGraphics = self.createAsset('enemyBullet', 'Enemy Bullet', .5, .5);
	self.move = function () {};
});
var Game = Container.expand(function () {
	var self = Container.call(this);
	var hero = self.addChild(new Hero());
	var enemies = [];
	var waveIndex = 0;
	var waveTimer = 0;
	var waveInterval = 300;
	var enemiesPerWave = 5;
	var heroBullets = [];
	var enemyBullets = [];
	hero.x = 2048 / 2;
	hero.y = 2732 / 2;
	LK.on('tick', function () {
		hero.move();
		waveTimer++;
		if (waveTimer >= waveInterval) {
			for (var i = 0; i < enemiesPerWave; i++) {
				var newEnemy = new Enemy();
				newEnemy.x = Math.random() * 2048;
				newEnemy.y = -100;
				enemies.push(newEnemy);
				self.addChild(newEnemy);
			}
			waveIndex++;
			waveTimer = 0;
		}
		for (var i = 0; i < enemies.length; i++) {
			enemies[i].move();
		}
		for (var i = 0; i < heroBullets.length; i++) {
			heroBullets[i].move();
		}
		for (var i = 0; i < enemyBullets.length; i++) {
			enemyBullets[i].move();
		}
	});
	stage.on('down', function (obj) {
		var pos = obj.event.getLocalPosition(self);
		hero.x = pos.x;
		hero.y = pos.y;
		hero.shoot();
	});
});

===================================================================
--- original.js
+++ change.js
@@ -22,14 +22,30 @@
 var Game = Container.expand(function () {
 	var self = Container.call(this);
 	var hero = self.addChild(new Hero());
 	var enemies = [];
+	var waveIndex = 0;
+	var waveTimer = 0;
+	var waveInterval = 300;
+	var enemiesPerWave = 5;
 	var heroBullets = [];
 	var enemyBullets = [];
 	hero.x = 2048 / 2;
 	hero.y = 2732 / 2;
 	LK.on('tick', function () {
 		hero.move();
+		waveTimer++;
+		if (waveTimer >= waveInterval) {
+			for (var i = 0; i < enemiesPerWave; i++) {
+				var newEnemy = new Enemy();
+				newEnemy.x = Math.random() * 2048;
+				newEnemy.y = -100;
+				enemies.push(newEnemy);
+				self.addChild(newEnemy);
+			}
+			waveIndex++;
+			waveTimer = 0;
+		}
 		for (var i = 0; i < enemies.length; i++) {
 			enemies[i].move();
 		}
 		for (var i = 0; i < heroBullets.length; i++) {