Egg Cube

The fourth boss in Sonic Advance 3, Eggman uses what is essentially a jack-in-the-box with a cockpit at the front. Inside the box, Gemerl emerges after every hit as either a clown, a wrecking ball, or a missle. The more hits Eggman takes, the more often he releases a group of three toy soldiers to hinder the player. The boss is defeated, not after eight hits, but by forcing the boss of the side of the arena. Technically, the boss could last forever if you turn the time limit off in the options.