Crystal Egg Zone is the seventh and final Zone in the 8-bit version of Sonic the Hedgehog 2. As with other Zones in this game, Crystal Egg consists of two standard Acts followed by a shorter third Act which contains the Zone's boss.
Crystal Egg Zone is perhaps the least visually threatening of Dr. Eggman's final bases, as it features bright, vibrant colors and crystal-clear walls, some of them even bearing the scientist's face. The boss arena is a different story altogether, as his stage is almost entirely black and mechanical. Spikes are plentiful here, as expected, and it is a very suitable last level.
The player can only get here by obtaining all of the Chaos Emeralds, otherwise the game will end after beating Mecha Sonic in Scrambled Egg Zone, leaving the player to view the bad ending. It is also possible to get here via the Level Select, but the bad ending would be displayed in this case as well.
||Rush through a land of sparkling crystal. Break through crystal blocks to find hidden treasure. Use a floating orb to sling you to higher ground.
Here you'll meet with Robotnik himself, in an arena he has prepared especially for you...
— Sonic the Hedgehog 2 US Game Gear manual
||??? — Similar to the Chopper piranha bots from Sonic 1; in this level they just "swim" horizontally through the air.