Role in the Subspace Emissary
After Solid Snake, Lucario, and Meta Knight kick all the Mr. Game & Watches out of the Halberd's control room, they fall to the bridge and dissolve into Shadow Bugs, which form into Duon. He is fought by Snake, Lucario, Fox, Zelda, Sheik, Peach, and Falco. It is basically a complete stage, Halberd Bridge. After it's defeated, it dissolves into Shadow Bugs, leaving behind a trophy of Mr. Game & Watch. It is reformed by Tabuu to face the heroes in the Great Maze, but is defeated again by the heroes, along with the other Nintendo villains (who have joined the heroes in order to stop and defeat Tabuu).
Duon is a two-sided robot on one set of wheels; one half being pink and possessing a head cannon and two arm cannons, and the other half being blue with a curved blade on his head tipped in light blue. Both sides have shoulder exhaust pipes which rockets (pink side) or mines (blue side) can be fired from (as well as their arm cannons). A character who gets behind Duon can trick it into blowing itself up with its own rockets. It rotates 180 degrees to change his attack strategy. The wheels it pivots on are the yin and yang symbols from Chinese belief, symbolizing balance and juxtaposition of two forces.
- Duon's design and color scheme bears a striking resemblance to the two legendary Pokémon Dialga and Palkia.
- Duon was formed by the essence that composes the inside of Mr. Game and Watch: shadow bugs. According to the storyline, Game and Watch is incapable of differentiating good and evil, and Tabuu manipulates Mr. Game and Watch in this way.