The Death Ball (デスボール) is a mini-boss encountered at the end of Death Egg Zone Act 2 in both Sonic & Knuckles and Sonic 3 & Knuckles before facing the Great Eggman Robo.
The Death Ball's form resembles a miniature Death Egg, which is protected by a rotating shield. Thanks to its bumper shield, Death Ball is immune to any direct attacks from the player; in fact, if the player glitches through the shield, they will find it doesn't even have proper collision. Its base periodically opens up, releasing small cars with three sets of spikes which then travel around the floor of the Death Egg. The only way to damage the boss is to hit it with the spiked side of the cars. The obvious method to do this is to use the gravity-switch tubes on the sides of the arena and timing it so they fall into the Death Ball, but Spin Dashing into a car that's upside-down relative to the current gravity will flip it into the air, which is far more efficient. Spike cars will be released right-side up relative to normal gravity, so staying in reversed gravity the entire battle lets the player make quick work of the boss.
A spike car left alone for too long will explode, sending its spikes out through the arena. The same will happen if a car hits the Death Ball with its wheeled side. In addition, Super Tails' Super Flickies can and will destroy the spike cars, preventing the player from damaging the Death Ball until Super form expires.
After hitting it with the cars 8 times, the Death Ball will be destroyed, and its destruction will damage the gravity-switch tube on the right, allowing the player to give chase to Dr. Eggman for the final showdown.