The first stage of each planet is divided by a mini-boss fight. This encounter is a large ship that fires large bullets in clusters at the player while standard enemy waves continue to spawn. The second half of the first stage ends with an encounter with the "comet" which will share the same colour as the planet being defended (blue for Earth, yellow for Venus, Red for Mars, and so on). The comet boss will open a small section of its exterior, revealing a small patch of circuitry from which a bullet will spawn. When the player destroys 5 such openings, the comet will explode and allow the player ship to enter the comet, starting stage two for that planet.