Duon is a giant, double faceted machine on one set of wheels and two different patterns of attack (one for each side). A character unique to Super Smash Bros. Brawl, it is made of the stuff of Mr. Game & Watch and attempts to ambush the Smashers on the bridge of the Halberd, comprising one of the single greatest threats short of Tabuu himself.
Now depending on which side is facing you determines what type of attacks you’ll receive. The blue side will attack with physical, melee-based attacks, whereas the pink side will shoot you with long-ranged weaponry. Note that at any time during the battle, Duon can turn around, changing which side is attacking you. There are several moves used regardless of which side is facing you: Sometimes Duon will rear up and charge you on its wheels across the bridge. You’ll have to quickly double jump and even then you’ll barely be able to clear it (you may need an up-B move as well)—Fox is the best for this. If you stand too close to the machine, it’ll start spinning, grindings its wheels into the ship—and into you, if you’re close, and this attack does have a vacuum effect. The thing can also leap high into the air and land with a devastating smash on the other side, so be clear out of the way when it does.
If you’re confronted by Duon’s blue side, it can slowly roll toward you and then slice with three slashing thrusts in combination. Draw it to you, then quickly leap and air dodge away for all three to miss you; it can also execute a powerful single vertical uppercut. Sometimes it’ll smash its bladed head into the ground, knocking you very far back if it connects with you. It does have one ranged attack, a series of mines that it’ll throw up into the air, which will fall to the ground, exploding when they hit. Try to weave in and out of them and do your best to stay on one side of the area when they’re falling. The pink side is perhaps more dangerous. It can shoot a wide, circular, and fast array of lasers. It can also shoot pink lasers in front of it and toward the ground—these can be reflected back on Duon for good damage. Then there are the blue lasers, three of them shot in succession that cannot be reflected and require very fancy footwork in dodging (be sure to throw in an air dodge too). It’ll also shoot three balls of fiery energy from its head. Duon’s last attack is a barrage of homing missiles. These are tricky to avoid, and air dodging will do you little good. One trick you can use is to guide the missiles toward Duon itself (preferably by double jumping over the tall boss) as those missiles will hurt Duon quite badly.
Duon is widely considered the hardest boss in all of Brawl, and for good reason. Its attacks are very damaging, tough to avoid, and the machine itself moves fast and leaves little room open for your attacks. Fox is by far your character of choice here. He’s better than most other characters at leaping over the thing when it charges you and when you need to clear it while missiles are following you into Duon. He can also stand calmly at a distance and fire away with his Blaster, and his speed is a godsend against the formidable array of Duon’s attacks. Fox’s most useful role, however, in this fight is his Reflector that he can use against the pink side when it fires the pink laser. Stand relatively close to the boss and watch that life meter seep away when reflecting those lasers back for great damage. The bigger characters such as DK, Charizard, Bowser, and Ike can whittle away Duon’s life meter with brute efficiency too thanks to their powerful attacks, but you’ll likely be receiving a good deal of damage yourself in the process. It’s almost impossible to fight this boss well without some sort of long-range attack.
Duon appears as the sole battle at Battleship Halberd Bridge, and you initially fight it with Peach, Sheik, Fox, Falco, Lucario, and Snake.