Sonic advance 2. I love destroying eggman in the last level. First three bosses are easy, but the forth where he drops bombs I find slightly difficult. The other bosses are easy to destroy.
The final zone of sonic advance 1, I play as knuckles, and when I fight eggman, I jump into him, then using knuckles gliding abilities, I smash into him a second time, I do it again, and he's destroyed.