Master Hand is a boss character in Kirby series. He and his counterpart Crazy Hand have appeared in Super Smash Bros. series too. Inhaling him gives Kirby the ability Smash based on his moveset in Super Smash Bros. series.
Master Hand is, like his name says, a hand, an animated hand. It can fly through air and perform many punches, slaps and some special attacks, like shooting bullets, laser beams and sweeping through stage.
In Kirby & the Amazing Mirror Master Hand is, together with Crazy Hand, the main boss of world 9, Candy Costellation. In Super Smash Bros. series he appears as a final boss of hte classic mode and in 1 event match in Melee.