* Buzz system : each time the nose or wings of the player's ship grazes a bullet or an enemy, this counts as one "buzz" (only the very center of the ship is vulnerable). For each buzz, a meter at the top of the screen increases by a small increment. When the meter fills up through repeated buzzing, the ship 'levels up' and experiences a brief moment of invincibility. The player can use this short period to risk buzzing more bullets to reach the next level-up, or to avoid particularly difficult bullet patterns. To aid buzzing bullets multiple times, the ship can be repeatedly spun on its axis by rapidly waggling the joystick left and right.