Mario is a Zenith and Luigi is a Heretical Scourge. Yoshi is a Wyld-mutated intelligent claw strider.
OctavianBowser is a Second Circle demon, and his minions are the First Circle demons he's created.
Toads are mortals, and Princess Peach can vary pretty wildly in between games. In some, she's a ronin, in others, she's barely more then an extra.
Boos are ghosts, yeah. Wario is a Slayer. Dunno about Walugi. Fawful is a Defiler with Solar circle sorcery.
Hm. This could be a fun campaign.