This is the one time Eggman did what he otherwise could never do: defeat Super Sonic.

Big Arm, the final boss of the Sonic 3 portion of the game.

If nothing else, it's an excellent display of teamwork between Sonic and Tails.

The epic aerial battle at the end of Marble Garden Zone.

Rather than being a conventional boss battle, you're required to race him through the stage, maneuvering past obstacles on the course and his attacks against you. Even as a Breather Boss, he and the following fight against Robotnik are extremely harrowing since, prior to this, you could survive indefinitely on a single ring if you knew how, but now there is no room for error. The final zone is simply two boss fights, the first of which is a Breather Boss in the form of an early version of Metal Sonic.

You also get no rings, meaning you die in one hit.

More so when fighting him for the first time and finding that unlike every single previous boss in both games, he doesn't go down in 8 hits, but in 12.

This was where Robotnik showed just how difficult he could really be, despite the fact that you've spent the last seven or so levels kicking his ass. He's blue, he's fast, and he's met lots of awesome bosses over the years.

Metal overlord vs perfect chaos