Egg Saucer

The Egg Saucer is the machine boss of Sky Canyon in Sonic Advance 2.

Sonic the Hedgehog
When reaching this boss as Sonic the Hedgehog, the boss turns out to be Knuckles the Echidna. After destroying the machine, Knuckles, angered, runs after Sonic with oil all over him. It was then revealed that Eggman tricked Knuckles again and Sonic runs off to continue his adventure. Knuckles then swears revenge on Eggman for tricking him and Knuckles is then playable. If Sonic goes back through the stage, the boss will be Eggman instead of Knuckles.

Other characters
If playing the stage as any other character, the boss will be Eggman.