Duon

Duon is a boss that is encountered late in The Subspace Emissary. It doesn't hail from any particular series and is unique to Super Smash Bros. Brawl, though it does bear a slight resemblence to Dialga and Palkia.

After Snake, Meta Knight and Lucario kick all of the Mr. Game & Watches off of the Halberd's bridge, they dissolve into Shadow Bugs, which form into Duon. Duon is a large robot with two upper bodies protruding from its base. One of these bodies has a blade for a head, while the other has a laser. When one head takes damage, it turns 180 degrees and presents its other head. Tabuu sends Duon to waste the heroes' time when he sends them into a maze of different worlds.