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 bullet = new HeroBullet();
		bullet.x = this.x;
		bullet.y = this.y;
		heroBullets.push(bullet);
		self.addChild(bullet);
	};
});
var EnemyWave1 = Container.expand(function (enemyCount) {
	var self = Container.call(this);
	self.enemyCount = 10;
	var enemyGraphics = self.createAsset('enemyWave1', 'Enemy Wave 1 character', .5, .5);
	self.move = function (heroX, heroY) {
		var dx = heroX - this.x;
		var dy = heroY - this.y;
		var magnitude = Math.sqrt(dx * dx + dy * dy);
		this.x += dx / magnitude * 2;
		this.y += dy / magnitude * 2;
	};
});
var EnemyWave2 = Container.expand(function (enemyCount) {
	var self = Container.call(this);
	self.enemyCount = 3;
	var enemyGraphics = self.createAsset('enemyWave2', 'Enemy Wave 2 character', .5, .5);
	self.move = function (heroX, heroY) {
		var dx = heroX - this.x;
		var dy = heroY - this.y;
		var magnitude = Math.sqrt(dx * dx + dy * dy);
		this.x += dx / magnitude * 2;
		this.y += dy / magnitude * 2;
	};
});
var EnemyWave3 = Container.expand(function (enemyCount) {
	var self = Container.call(this);
	self.enemyCount = 4;
	var enemyGraphics = self.createAsset('enemyWave3', 'Enemy Wave 3 character', .5, .5);
	self.move = function (heroX, heroY) {
		var dx = heroX - this.x;
		var dy = heroY - this.y;
		var magnitude = Math.sqrt(dx * dx + dy * dy);
		this.x += dx / magnitude * 2;
		this.y += dy / magnitude * 2;
	};
});
var EnemyWave4 = Container.expand(function (enemyCount) {
	var self = Container.call(this);
	self.enemyCount = 20;
	var enemyGraphics = self.createAsset('enemyWave4', 'Enemy Wave 4 character', .5, .5);
	self.move = function (heroX, heroY) {
		var dx = heroX - this.x;
		var dy = heroY - this.y;
		var magnitude = Math.sqrt(dx * dx + dy * dy);
		this.x += dx / magnitude * 2;
		this.y += dy / magnitude * 2;
	};
});
var EnemyWave5 = Container.expand(function (enemyCount) {
	var self = Container.call(this);
	self.enemyCount = 1;
	var enemyGraphics = self.createAsset('enemyWave5', 'Enemy Wave 5 character', .5, .5);
	self.move = function (heroX, heroY) {
		var dx = heroX - this.x;
		var dy = heroY - this.y;
		var magnitude = Math.sqrt(dx * dx + dy * dy);
		this.x += dx / magnitude * 2;
		this.y += dy / magnitude * 2;
	};
});
var HeroBullet = Container.expand(function () {
	var self = Container.call(this);
	var bulletGraphics = self.createAsset('heroBullet', 'Hero Bullet', .5, .5);
	self.move = function () {
		this.y -= 5;
	};
});
var EnemyBullet = Container.expand(function () {
	var self = Container.call(this);
	var bulletGraphics = self.createAsset('enemyBullet', 'Enemy Bullet', .5, .5);
	self.move = function (heroX, heroY) {
		var dx = heroX - this.x;
		var dy = heroY - this.y;
		var magnitude = Math.sqrt(dx * dx + dy * dy);
		this.x += dx / magnitude * 2;
		this.y += dy / magnitude * 2;
	};
});
var Game = Container.expand(function () {
	var self = Container.call(this);
	self.getEnemyCountForWave = function (waveIndex) {
		switch (waveIndex % 5) {
			case 0:
				return 10;
			case 1:
				return 3;
			case 2:
				return 4;
			case 3:
				return 20;
			case 4:
				return 1;
		}
	};
	var hero = self.addChild(new Hero());
	var enemies = [];
	var waveIndex = 0;
	var maxWaveCount = 5;
	var waveTimer = 500;
	var waveInterval = 500;
	var heroBullets = [];
	var enemyBullets = [];
	hero.x = 2048 / 2;
	hero.y = 2732 / 2;
	LK.on('tick', function () {
		hero.move();
		if (waveIndex < maxWaveCount) {
			waveTimer++;
		}
		if (waveTimer >= waveInterval && waveIndex < maxWaveCount) {
			for (var i = 0; i < self.getEnemyCountForWave(waveIndex); i++) {
				var newEnemy;
				var enemyCount = self.getEnemyCountForWave(waveIndex);
				switch (waveIndex % 5) {
					case 0:
						newEnemy = new EnemyWave1(enemyCount);
						newEnemy.x = Math.random() * 2048;
						newEnemy.y = 0;
						break;
					case 1:
						newEnemy = new EnemyWave2(enemyCount);
						newEnemy.x = Math.random() * 2048;
						newEnemy.y = 2732;
						break;
					case 2:
						newEnemy = new EnemyWave3(enemyCount);
						newEnemy.x = Math.random() * 2048;
						newEnemy.y = Math.random() * 2732;
						break;
					case 3:
						newEnemy = new EnemyWave4(enemyCount);
						newEnemy.x = Math.random() * 2048;
						newEnemy.y = Math.random() * 2732;
						break;
					case 4:
						newEnemy = new EnemyWave5(enemyCount);
						newEnemy.x = Math.random() * 2048;
						newEnemy.y = Math.random() * 2732;
						break;
				}
				enemies.push(newEnemy);
				self.addChild(newEnemy);
			}
			waveIndex++;
			waveTimer = 0;
		}
		for (var i = 0; i < enemies.length; i++) {
			enemies[i].move(hero.x, hero.y);
		}
		for (var i = 0; i < heroBullets.length; i++) {
			heroBullets[i].move();
			if (heroBullets[i].y < 0) {
				heroBullets[i].destroy();
				heroBullets.splice(i, 1);
			}
		}
		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
@@ -4,10 +4,11 @@
 	self.move = function () {};
 	self.shoot = function () {
 		var bullet = new HeroBullet();
 		bullet.x = this.x;
-		bullet.y = this.y - this.height / 2;
-		this.parent.addChild(bullet);
+		bullet.y = this.y;
+		heroBullets.push(bullet);
+		self.addChild(bullet);
 	};
 });
 var EnemyWave1 = Container.expand(function (enemyCount) {
 	var self = Container.call(this);
@@ -72,12 +73,9 @@
 var HeroBullet = Container.expand(function () {
 	var self = Container.call(this);
 	var bulletGraphics = self.createAsset('heroBullet', 'Hero Bullet', .5, .5);
 	self.move = function () {
-		this.y -= 10;
-		if (this.y < -this.height) {
-			this.destroy();
-		}
+		this.y -= 5;
 	};
 });
 var EnemyBullet = Container.expand(function () {
 	var self = Container.call(this);
@@ -116,11 +114,8 @@
 	var enemyBullets = [];
 	hero.x = 2048 / 2;
 	hero.y = 2732 / 2;
 	LK.on('tick', function () {
-		for (var i = 0; i < heroBullets.length; i++) {
-			heroBullets[i].move();
-		}
 		hero.move();
 		if (waveIndex < maxWaveCount) {
 			waveTimer++;
 		}
@@ -160,50 +155,15 @@
 			}
 			waveIndex++;
 			waveTimer = 0;
 		}
-		var grid = [];
-		for (var i = 0; i < 10; i++) {
-			grid[i] = [];
-			for (var j = 0; j < 14; j++) {
-				grid[i][j] = [];
-			}
-		}
 		for (var i = 0; i < enemies.length; i++) {
-			var gridX = Math.floor(enemies[i].x / 204.8);
-			var gridY = Math.floor(enemies[i].y / 195.14);
-			if (!grid[gridX]) grid[gridX] = [];
-			if (!grid[gridX][gridY]) grid[gridX][gridY] = [];
-			grid[gridX][gridY].push(enemies[i]);
-		}
-		for (var i = 0; i < 10; i++) {
-			for (var j = 0; j < 14; j++) {
-				for (var k = 0; k < grid[i][j].length; k++) {
-					for (var l = k + 1; l < grid[i][j].length; l++) {
-						if (grid[i][j][k].intersects(grid[i][j][l])) {
-							var dx = grid[i][j][l].x - grid[i][j][k].x;
-							var dy = grid[i][j][l].y - grid[i][j][k].y;
-							var distance = Math.sqrt(dx * dx + dy * dy);
-							if (distance < grid[i][j][k].width / 2 + grid[i][j][l].width / 2) {
-								var overlap = grid[i][j][k].width / 2 + grid[i][j][l].width / 2 - distance;
-								dx /= distance;
-								dy /= distance;
-								grid[i][j][k].x -= overlap / 2 * dx;
-								grid[i][j][k].y -= overlap / 2 * dy;
-								grid[i][j][l].x += overlap / 2 * dx;
-								grid[i][j][l].y += overlap / 2 * dy;
-							}
-						}
-					}
-				}
-			}
-		}
-		for (var i = 0; i < enemies.length; i++) {
 			enemies[i].move(hero.x, hero.y);
 		}
-		for (var i = heroBullets.length - 1; i >= 0; i--) {
+		for (var i = 0; i < heroBullets.length; i++) {
 			heroBullets[i].move();
-			if (heroBullets[i].isDestroyed) {
+			if (heroBullets[i].y < 0) {
+				heroBullets[i].destroy();
 				heroBullets.splice(i, 1);
 			}
 		}
 		for (var i = 0; i < enemyBullets.length; i++) {