Wart is the king of
bad dreams in
Nintendo's
Super Mario Brothers 2 video game (and its Japanese origin game,
Doki Doki Panic). He's a large green
frog, he wears a
robe, and he hangs out in a room with a machine that creates
vegetables. This is not a smart move on his part, however, as this room leaves him with no escape from
Mario and friends, plus he is deathly allergic to
vegetables, so why is he hanging out with them in the first place?
It makes no sense, but then again the entire adventure is nothing more than a
dream, so why should it?
Super Mario Brothers 2's story begins when Wart comes to the dreamworld of Subcon and enslaves its native population inside a vase. After plugging the vase with a cork, he sets loose a horde of monsters upon the land and promptly takes up residence in a castle in the sky. Mario, Luigi, Toad, and Princess Toadstool track him down in World 7, venture through his castle, and toss waves of turnips into his mouth, thus killing him. His main mode of attack is to blow bubbles at those who oppose him. Hmm, it occurs to me that Wart is not the badass that other Nintendo villains try to be.
At the end of Super Mario Brothers 2 Wart turned grey and died, freeing the land of Subcon from his oppression. However whenever the game is ported to a new platform he is reborn to fight another day. Look for him in Super Mario All-Stars, BS Super Mario USA, and Super Mario Advance. In fact, in BS Mario USA Mario is sent to Wart's chamber if he goes down a vase while in Subspace. Also look for him in the Super Mario Brothers comics where his sole appearance was as a shifty mattress salesman.
If you're looking for Wart outside of Super Mario Brothers 2, check out The Legend of Zelda: Link's Awakening and its DX version where he appears as Mamu, the frog master of soul singing. He teaches Link the toe-tapping song of life for a mere 300 rupees, then he goes on a concert tour. Link later uses the song to revive the flying rooster.
Presumeably Wart/Mamu is still on his concert tour, as he hasn't been seen since his Zelda cameo.