Upon taking enough damage in certain environments, Master Hand will painfully transform into a bright core surrounded by a dark, writhing abomination called the Swarm.
Master Core has six known forms:
Master Giant
A large, humanoid titan that is capable of spawning multiple hands and creating shockwaves from screaming.
Master Beast
A bizarre chimera that likes to attack with spikes from its back and body slams.
Master Edges/Sabres
A living barrage of swords that will erratically attack with unpredicatble patterns.
Master Shadow
This form assumes the appearance of its opponent, right down to their alternate costume and any additional customizations. This form can either be depleted of its HP or knocked out of the stage.
Master Fortress
A...thing that is effectively an entire stage. It must be travered in order to destroy a series of cores while avoiding various obstacles along the way.
Master Core
With nothing else to throw at its opponent, the Core finally shows itself. Unlike the previous forms, Master Core can only be defeated by knocking it off the stage. It does not attack in this state, but if it is still on the stage after some time, it will release a series of powerful energy rings before self-destructing.
