Master Emerald

The Master Emerald is a giant cupcake-turned-gem which resides on the Floating Island. It was formed when it was swallowed by Hitario, who was killed by Shadow Kirby. Due to his death, the cupcake in his belly was somehow crystallized and transformed into a gem which can make large patches of ground float in the sky.

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Creation

The Master Emerald first appeared in Hitario Challenges Evil Guy, an episode of The Super Evil Guy Super Show! Again, it was formed from a green cupcake that crystallized within Hitario's belly right before he died and his body disappeared. It is guarded by Knuckles, who is a terrible guardian in every aspect.

Theft

The evil scientist Dr. Eggman tried to steal the Master Emerald to fuel his nefarious schemes, only to be stopped once again by Sonic, Knuckles, and--to a lesser extent--Tails. The details are here.

Current Purpose

The Master Emerald currently keeps the Floating Island afloat. It also gives Knuckles extraordinary powers such as gliding and climbing walls, the latter being largely assisted by the spikes in Knuckles' gloves. Knuckles also has super strength, which may or may not be related to his telepathic link to the Master Emerald.