Nintendo has shrewdly delivered fan service with its announcements of characters and cameos for Super Smash Bros., from Mega Man to The Villager to Wii Fit Trainer. The latest tease, from creator Masahiro Sakurai, will appeal to fans of StreetPass' RPG Find Mii. It's the Dark Lord!
How can we be sure that's him? Well, the swinging cage that imprisons your Mii is a good enough tipoff. The only other context for his inclusion appears to be that he'll be in the 3DS version only. As what—an item, a hazard or even a playable character (doubtful)—no one yet knows.
Masahiro Sakurai|Super Smash Bros. Series [Miiverse, via IGN]