Crystal Egg Zone

General
Crystal Egg Zone is the seventh and last level of the Game Gear / Master System Sonic 2. It can be accessed only if you've successfully collected all the Chaos Emeralds in previous zones; otherwise, you get the Bad Ending after defeating Mecha Sonic in Scrambled Egg Zone. As with all other stages in this game, Crystal Egg Zone consists of two standard Acts followed by a shorter, third Act which contains the Zone's boss.

Crystal Egg is perhaps the least aestheticly offensive of all the final bases Eggman's constructed over the years; a zone of glassy, translucent architecture where even the spikes glow in rainbow hues. Rainbow hues of death. Blocks embossed with the Fat Man's pugnacious visage frequently conceal hidden walkways.

Last Boss
The scenery in Act 3 is more like we expect from the Doctor; hard, cold steel, and deadly electricity everywhere. The game's last boss takes place inside a lightning chamber, which Robotnik makes extra-fatal by throwing gyrating, flower-shaped energy bolts into the mix. However, the boss actually isn't that difficult if you stay inside the transport chutes until the chamber clears; at which point you can leap out, attack the Doc's position, and dive back in to safety before his attacks renew themselves.

His final machine destroyed, Eggman beats a hasty retreat down an escape chute. Sonic gives chase, but not quickly enough to stop the fat man escaping via teleporter. Just as the hedgehog thinks all is lost, Tails warps in through the teleport terminal; presumably thrown in there by Robotnik as a means of expediting his retreat. Cue Good Ending!