Duon is a two-sided robot on one set of wheels; one half is pink and has a head cannon and two arm cannons, and the other half is blue with two arm swords, and has a curved blade on his head. Both sides have shoulder exhaust pipes which rockets (pink side) or mines (blue side) can be fired from (though these can also be fired from the arm cannons). He rotates 180 degrees to change his attack strategy. The wheels he pivots on are the yin and yang symbols from Chinese belief, symbolizing balance and juxtaposition of two forces. He appears to have been created from Mr. Game & Watch.
Role in the Subspace Emissary
After Snake, Lucario, and Meta Knight kick all the fake Mr. Game & Watches out of the Halberd's control room, they fall to the bridge and dissolve into Shadow Bugs, which form into Duon, as a last resort to defend the Halberd. Duon is fought by Snake, Lucario, Fox, Sheik, Peach and Falco. It is basically a complete stage, Halberd Bridge. After he is defeated, he dissolves into Shadow Bugs, leaving behind a trophy of Mr. Game & Watch.
Duon charges forward quickly. Wheels do damage while tilted after dash. Might be used several times in a row with little pause in between.
Duon spins around. Vacuums (And pushes down if below edge).
Duon jumps up high and crashes down, then grinds in place (prevents close-range attacks). The jump goes farther across the field on higher difficulties, which, ironically, makes it easier to avoid on higher difficulties.
Duon turns around, switching active sides (Does damage). (After Mines or Missiles)
Pink Side active
Duon shoots pink lasers with a vertical-spread coverage. Can be reflected or absorbed. It will aim higher and a little back if above or behind Duon.
Duon shoots pink lasers at the ground in the front. These lasers can be reflected or absorbed.
Duon's head glows, and then shoots three blue bolts of electricity that will pierce though everything (including the field and Duon, but it doesn't hurt himself) except Pit's Mirror Shield. At higher difficulties, it will break shields, so dodging is far preferable. Cannot be reflected or absorbed.
Duon moves its non-weapon arm back to shoot four homing missiles. Will damage Duon if the missiles are lured back towards it; can also be detonated by projectiles. Always followed by a "shared attack".
Blue Side active
Duon slowly approaches, and then slashes three times when within range. He will turn around before slashing if jumped over.
Duon slams the blade on its head on the ground. An attack tricky to avoid.
Duon readies its arms, then slashes making a large red shockwave. Very powerful.
Duon launches several mines in the air. These can be detonated (won't hurt Duon) with vertical-based attacks, such as Pikachu's Thunder or a chucked item. Always followed by a "shared attack".
A robot with two upper bodies sharing one set of wheels. The blue-bodied half uses sword attacks, while the pink one uses lasers from his head and arms for offensive power. Whichever side is facing you will attack. Duon also threatens with homing missiles and the blade on top of the blue half.
Duon's name comes from the Latin word "duo", which means "two", referring to Duon's two sides.
Duon's appearance could be a reference to Dialga (blue) and Palkia (pink) from the Pokémon games.
Duon's appearance may also be a reference to the two main antagonists in the original Golden Sun who are Saturos (who wears blue and who has a few ranged moves, but attacks mostly with his sword) and Menardi (who wears pink and rarely uses her sword, preferring to attack using psynergy projectiles).
The wheel at the base shows the yin and yang symbol, depicting the differences between them, one using melee weapons whereas the other uses longer range weapons. However, it appears that the white circle in the black part of the symbol is replaced by more black, perhaps indicating that the machine is pure evil or more bad than good.
Duon is deemed by many as the hardest Boss Battles boss because of its incredibly damaging attacks and their very high knockback as well as the difficulty to avoid them.
On intense difficulty, a trophy stand rarely appears, so Duon's trophy is very hard to grab and it requires very good timing to throw it. Duon also quite commonly pushes the Trophy Stand off the stage if it is not grabbed quick enough. For this reason, it may be a better idea to attempt to capture the boss on a lower difficulty, where it is easier to stay alive while waiting for the trophy stand.
There is an invisible platform between Duon's two halves, making Duon one of only two bosses that a character can actually stand on, the other being Porky Minch. This also means that characters can't pass through the lower half of Duon's body.
You can lure Duon's missiles into its body, it is easier on harder difficulty due to the missiles accuracy increase the higher the difficulty.
If Duon is defeated just after he fires his missiles, the missile will explode in mid-air during his death animation.
Duon is the only boss made out of Shadow Bugs.
Duon is one of the two opponents made out of shadow bugs that were in a previous form (the other is dark Peach/Zelda).