The Moai, also known as Easter Island heads, were head-shaped statues that decorated Easter Island, and were in fact the guardians of the Easter Island Hellmouth.
While performing a ritual to open the Eastern Island Hellmouth, the Courtesan demon Morgan inadvertently awakened the Moai, who revealed themselves to have full bodies submerged under the Earth. Spike, Morgan, and his crew managed to fight off and destroy the Moai, albeit at the cost of Spike's ship.