King Ka-thunk

King Ka-thunk is a boss that appears in Super Mario 3D World as the boss of World 5-Castle: King Ka-thunk's Castle. He is a small, blue metal square with red feet and detached red hands. He also has five spikes on the front and his back is pink and fleshy with a bandage on it. King Ka-thunk floats in the middle of another, larger Ka-thunk.

He serves as the boss of World 5. His main attack moving around the Ka-thunk before finally stopping in one of the corners. After this, the ground that King Ka-thunk will fall on glows red before he crashes into the ground, damaging any players caught under the Ka-thunk. To damage King Ka-thunk, the player has to jump on his backside while he is face down. After each hit, two of the arena's corners will fall off, and King Ka-thunk will become faster and more erratic. Once three hits are landed, King Ka-thunk is defeated, and the Warp Box to the Goal Pole is revealed.

King Ka-thunk later reappears as one of the bosses in World Flower-12: Boss Blitz. However, his strategy has not changed since the first battle.