False Peach is made of Shadow Bugs.
Subspace Peach is one of the bosses you encounter in The Subspace Emissary story in the video game Super Smash Bros. Brawl. She looks like Princess Peach, only covered in some black-purple mist. Unlike Peach, she used the Dark Cannon.
Role
After Kirby left Peach for a few seconds, Bowser turned Peach into a trophy and had Shadowbugs engulf her. Shortly after this, Subspace Peach prepares to turn Mario and Pit into trophies, but is stopped by Link and Yoshi.
(NOTE: This only occurs if you save Peach at the Midair Stadium. If you saved Zelda, Subspace Peach will be replaced by Subspace Zelda.)
Later, Subspace Peach and Subspace Zelda appear to stop Meta Knight, Lucario, and Solid Snake from freeing the princesses, but are defeated.
Pysical Apperance
Much like Peach, only with glowing eyes and all purple and covered by an all purple, misty aura.
Trivia
Subspace Peach is one of the only bosses you don't beat in Boss Battle (the other 2 being Subspace Zelda & Subspace Diddy Kong).