Shadow the Hedgehog

Shadow the Hedgehog (シャドウ・ザ・ヘッジホッグ, Shadō Za Hejjihoggu), also known as "The Ultimate Lifeform", is a character from the Sonic franchise. He first appeared in Sonic Adventure 2 for the Dreamcast console. Shadow was created for the "Ultimate Good" but government thought Professor Gerald, Shadow's creator might use him for evil, so they sent G.U.N. soldiers to shut down the Space Colony ARK. Shadow is the rival to Sonic, and has his own game that came out for all 3 sixth-generation with the name of "Shadow The Hedgehog". He is a playable character in super Smash Flash and Super Smash Flash 2.

In Super Smash Flash
Shadow made an appearance in Super Smash Flash as an unlockable character. He was unlocked only after Sonic, Knuckles, and Tails have cleared Adventure Mode.

In Super Smash Flash 2
Shadow was previously confirmed to once again appear in Super Smash Flash 2 as now the only unlockable character of the Sonic universe. His status is currently unknown.