Isaac. Forget his swordsmanship, magical weapons, psychic powers, earth magic, healing arts, summoning skills, hovering, teleportation, time control, or ability to slap you with his mind; it's all about that scarf! It took over two years and 700+ developers to implement Isaac's scarf in Brawl, and the only reason that he's not playable is because they all failed. Sure, he's an AT and still has his scarf, but to reveal Isaac's scarf in its full glory would be an affront to the gods themselves!
I'm serious.
It's a nice scarf.