Shadow the Hedgehog

Shadow also known as "The Ultimate Lifeform" 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".

Super Smash Flash
Shadow made an appearance in Super Smash Flash as one of the 28 characters. He was unlocked only after Sonic, Knuckles and Tails all cleared Adventure Mode.

Super Smash Flash 2
Shadow once again appears in SSF2 as an unlockable character. He will be faster and stronger than in SSF.

Other
Entrance: A black hole appears and Shadow comes out of it

Taunt: Takes a serious pose

Wins: Takes out a Chaos Emerald

Loses: Touches his head like he is in pain