- For the Badniks with the same name, see Egg Saucer (Sonic Blast).
The Egg Saucer appears to be a giant wheel with a grey tire and is decorated with alternating of yellow and brown-colored strips around its circumference. It has three contraptions mounted on it which can revolve around about the wheel's center: a cockpit, a laser cannon and a giant hand. The cockpit and the cannon is blue and orange, and the hand is mostly gray with some blue and orange dots on it. Each of these contraptions are mounted on a metallic stand on the wheel, which is mostly grey with a blue spherical glass on either end, a smaller blue spherical unit on the center, and orange borders with spikes underneath.
The machine will stay to the right of the stage whose three components rotate clockwise throughout the entire fight. The laser cannon, will fire two lasers in succession (though the first laser does not deal any damage) though it can optionally be destroyed. The hand serves as the main threat of the boss fight as it cannot be destroyed unlike the cannon. It will swing down, trying to chop the character, or it will do an open-hand slap, which results in an instant death. After the slap, the hand will stay open for a while. Touching it in this state will also result in an instant death. The cockpit has no defenses , but it can be hard to hit since it has to be hit at the very top. If hit from the bottom, the character will sustain damage.
Egg Saucer later reappears in the XX stage, the boss rush of the game. It has all attacks from the previous time, as each of parts take only one hit, and the cockpit can be damaged by doing only three hits to destroy the machine.
- When playing the boss for the first time as Sonic, Knuckles is the pilot of the Egg Saucer while the act plays the exclusive "Knuckles Boss" BGM (until hitting the boss enough times to initiate pinch mode). In subsequent battles with this boss though for the rest of the game, Dr. Eggman is the pilot.
- According to the Prima Strategy Guide for Sonic Advance 2, the Egg Saucer was the most expensive weapon in Eggman's R&D expenses, which also resulted in the next two Eggman machines being flops.
- Egg Saucer is pointed out by fans to be the hardest boss in the game, due to the invisible laser attack from the cannon, and one attack by the hand part of the vehicle, which can cause instant death even if the player has rings.