Isle of the Dead

The Isle of the Dead is a warp zone found in 3-4, widely considered to be the hardest stage in the game. It consists of you running through a maze of skulls with a Paunchy Chops chasing you, while trying to avoid the other enemies spread around the stage. The 2 other enemies encountered in this stage are Mortobbys and Bone Nibblers.

After reaching the end of the stage, you're taken to Satan's Lair, where Satan decides to offer you a chance to join him in his quest to rule the world. If you accept, you get infinite lives (usable in ludicrous mode as well), and if you decline, you get 20,000 coins and have to fight him. After you get out of Satan's Lair you're taken to 3-5.