4. Final Boss (Sonic & Knuckles with Sonic 3)
Well, what can you say about this? After one of the finest platform games ever made (accessed by plugging the Sonic 3 cart into the top of Sonic & Knuckles and starting from the beginning), you'd expect a suitably grandiose finale. And there is one. You get to face this monster. Look at the size of it! Those fingers alone are twice as tall as Sonic.
Why it's mad: Well, Sonic can break those fingers, at which point the boss starts to fall away. It's so big, it appears to have weight in outer orbit. It's also stupid enough to try to clamp down on Sonic while he's revving up a spin dash, which doesn't hurt the spiky one in the slightest. Finally, after this attack fails, Robotnik resorts to using the power of the master emerald to fire a massive laserbeam at Sonic, exposing the most obvious design flaw since the Death Star's exhaust port, which exposes the emerald to direct attack. Cretin.