Max Omega wrote...
Sephiroth
Sephiroth's a little bitch!
Cosplay a REAL man, Like Kefka!
As for challenging cosplay, try one from the later Seiken Densetsu (Mana) games, or Saber from Fate/Stay Night in her full battle gear (armor included).
Or if you want to be epic, take two characters and cross them into one: