Shovel Knight. They are attached to the ceiling with chains above pits throughout the Iron Whale. When Shovel Knight draws near, they fall swiftly down and ratchet slowly back up. When they are falling, they can strike and damage Shovel Knight, often knocking him into a pit. When they are retracting, Shovel Knight can jump on the cross-beam and use it as a platform.
Their falling can damage the player, however if minor enemies get hit instead, it is an instant kill, even for some strong enemies immune to normal attacks.