The Final Fight

Final Fight, as seen in the Sega Mega Drive/Genesis version of Sonic 3D: Flickies' Island.

The true last level of Sonic 3D: Flickies' Island, the whole level of Final Fight is one boss, with Robotnik using a multi-capable robot to destroy you. This boss required an astounding 12 hits to kill, making it the most challenging boss in the game. This level is only accessible if you finish the game with all seven emeralds.

Strategy

Get a few rings to start out with. The goal is to hit Robotnik and his robot when they move into the platform. The first obstacle is dodging finger lasers. This is very frustrating, especially because some games have a glitch where he rapidly fires them for a few seconds so fast they are next to impossible to dodge. Hit him the same way as before, except what he does to Sonic changes. He may shoot flames at you, he'll try to squish you, he'll use both of his hands to crush you, he'll shoot ball-bearing, etc. Just keep on avoiding and hitting him until he's dead.