From the post:
The Grave Golem is, essentially, a large chunk of graveyard that has been animated by the Resurrectionists to serve as a heavy enforcer. During battle, a Grave Golem can sink into the earth and reappear a few moments later halfway across the battlefield, provided that there is a corpse for the golem to form around. That something so large could move so quickly often comes as a surprise to the golem's enemies, many of whom end up either battered to death by its massive Tombstone Fists or buried in a landslide of corrupted earth and grasping skeletal arms.
Source
