Ka-thunks are enemies that appear only in the courses King Ka-thunk's Castle and Bowser's Lava Lake Keep in Super Mario 3D World. Ka-thunks resemble metal
blue square frames covered in spikes which hurt the player upon contact. They either spawn in small crevices and move along a set path until they fall into an abyss, or appear moving in a looping path. Some simply flip side to side. They function similarly to Tox Boxes, as they move along paths, and the player must avoid them by using the hollow space in the middle. They cannot be destroyed by any means, including invincibility, excluding a pair of Ka-thunks in Bowser's Lava Lake Keep which disappear upon defeating a pair of Hammer Bros.
King Ka-thunk holds onto a larger Ka-thunk during his battle.