Also known as: クレイジーハンド
If his name didn't tip you off, this is the crazed counterpart to Master Hand, often serving as a true final boss in the Super Smash Bros. games (starting with Melee) alongside his more sane brother.
His role in the universe is even less clear than Master Hand's, though it is stated that he is the destructive spirit to Master Hand's creative spirit.
He also runs a side joint called Crazy Orders, where he bargains participants with rewards for increasing challenges and a final confrontation with him.