Dark Chylde (Magik)
The character Magik (Marvel Comics' New Mutants) in her demonic persona. She did a great job on this and I loved her "hooves" as that was a very clever idea!
The cosplayer is TresWildCosplay.
UPDATE: Dark Chylde was featured in Uproxx's A Compendium of Cool Comics Cosplay: Best of 2012!! The. Best. Of. 2012?!! Whoa... *feels faint... thud* I forwarded this info to Tres Wild but for myself, many thanks go out to Angelophile, Uproxx, and Gamma Squad cosplay