The Crystal Egg Zone boss is the true final boss of the 8-bit versions of Sonic the Hedgehog 2, fought at the end of Crystal Egg Zone. Unlike all the other bosses in the game, it is an unnamed mechanical arena operated by Dr. Eggman.
After the unusual reflective images of Eggman's fortress in the first two acts of Crystal Egg Zone, the scenery in Act 3 changes to a more customary final level - hard, cold steel, and deadly electricity everywhere. The game's last boss takes place inside a lightning chamber, which Eggman makes extra-fatal by shooting gyrating, flower-shaped energy bolts into the open space in front of him. At set intervals, Eggman will activate the electrical conduits all around the arena which will fatally zap Sonic. However, the boss actually isn't that difficult if Sonic stays inside the transport chutes that surround the arena until the chamber clears, at which point he can leap out, attack the scientist's cockpit, 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 Eggman from escaping via a teleporter. Before Sonic leaves, Tails will warp in through the teleport terminal.
Eggman escapes via a teleporter
Tails appears in the teleporter
The stars themselves cheer at Sonic's victory
Official artwork of Crystal Egg Zone boss.