King Ka-thunk

King Ka-thunk (known as King Kathunk in the British English version of the original game) is a boss that appears in Super Mario 3D World and its Nintendo Switch port Super Mario 3D World + Bowser's Fury as the boss of World 5-Castle: King Ka-thunk's Castle. He is a small, blue metal square with red shoes and detached red hands. He also has five spikes on the front (one of which is positioned like a beak right below his eyes) and his back is pink and fleshy with an X-shaped bandage over it. King Ka-thunk floats in the middle of another, larger Ka-thunk frame that his hands hold on to.

He shares his boss theme with Boss Brolder and Motley Bossblob.

He serves as the boss of World 5. His main attack is moving around the Ka-thunk frame 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 him or his frame. To damage King Ka-thunk, the player has to jump on his backside while he is facing down. Oddly enough, he is not damaged if a player is thrown onto his weak spot by another player. 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, several circles of Coins appear, 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 with the exact same strategy from his first battle in World 5.