Skullyrex

The Skullyrex is an undead skull enemy that first appeared in Donkey Kong Country Returns and its 3DS port. Skullyrexes are basically Skellirexes without any body at all, and are smaller in size. They hop around from left to right, and they can be taken out with any kind of attack. A Skellirex behaves exactly like a Skullyrex when it loses its body.

Reference
Skalettorex