Skull Warrior

the skull warriors are Kulta's minions that reside in the Ancient City on Okoto.

Lego.com description
The Skull Warriors are the rank and file of Skull Grinder’s army. Animated by his dark power, these skeletons shamble relentlessly into battle, and only a fool does not fear the Skull Warriors. What they lack in strength, they more than make up for through numbers. Even when knocked down, these fearless fighters will keep coming back to freeze the bones of all but the bravest heroes.

History
A group of Skull Warriors tried to stop the Toa at the gate of the Ancient City but were all defeated by the Toa.