Ultra Sword is an upgraded version of Sword. Unlike other Super Abilities, the Ultra Sword is also used to finish off two bosses - Grand Doomer and Magolor's first phase (as well as their EX versions). It also is used in the penultimate level of the game to defeat every mid-boss (except Super Bonkers), obliterating each in one chop.
Kirby sweeps a sword, cutlass, kendo stick, meat cleaver, Galaxia, bluefin tuna, or a golden paper fan in a wide arc in front of him.
In Super Smash Bros. for Wii U, Kirby wielding the Ultra Sword appears as a collectible trophy.
Unlike the other Super Abilities, Ultra Sword will randomly change the weapon used when attacking.
This makes Ultra Sword one of the few abilities to have a multi-form attack; the others being Stone, Archer, and Circus.
Upon using Ultra Sword to defeat Grand Doomer] (EX), he always initially uses the cutlass. This is most likely a reference to the fact that it was his default sword before the game officially came out.
The Ultra Sword is the only Super Ability that has a revamped song when acquired which is only used in two instances: the Grand Doomer (EX) battle and the final stage of Dangerous Dinner.
In the final phase of the Magolor battle, for one of his moves, he uses two darkened Ultra Swords. In Extra Mode, Magolor Soul instead uses two darkened Galaxias for the attack, possibly as a reminder that Extra Mode makes enemies stronger.
In Kirby: Planet Robobot, the Stoneability will rarely produce a Golden Statue of Ultra Sword Kirby wielding the Bluefin Tuna.
In BOXBOXBOY!, the comic Kirby's Closet depicts Qbby trying on Kirby's Ultra Sword Ability Hat and carrying the sword itself. The comic ends with him turning around to find Kirby watching him.
For Kirby's Final Smash, he swings a sword that's waaay bigger than he is. If the first swing hits, he'll keep going with a combo of lightning-fast slices, dealing tons of damage. For the last swing, the sword grows even larger and launches any victims. Make sure that first swing hits, though, or nothing else will happen!”