As its name implies, the Bone Golem is a golem made entirely of bones that can be configured in several different ways. Destroying one form causes it to reassemble into the next one:
At first, the Bone Golem will acquire the form of a centaur-like monstrosity that has two pairs of arms and six hind legs. It will slowly pace back and forth and is able detach one of its arms and reattach its segments to the other, sending it forward for a ranged attack.
At one point, it may stop for a moment, turn its color to an incandescent yellow tone, and breath a stream of fire forward.
After one third of its health has been depleted, the golem's bones will be sent flying and reassemble into a strange-looking winged creature on their way down. Once again, only its head is vulnerable during this form.
It has two attacks:
It makes a slow, straight pass from one end of the screen to the other while continuously dropping exploding skulls, all this while swinging its long tail back and forth in an attempt to inflict contact damage.
It starts flying up and down in a wave like manner, and makes a faster pass to the other end of the screen while swinging its tail.
Once two thirds of its health have been depleted, the golem will break apart and reassemble one last time, acquiring its third and final form: a turtle-like mass of bones that will start ramming from one side of the room to the other at great speed. Each time it is struck, it will stop for a brief moment. Care must be taken not to miss any hits, as even a single error can let it get over the player and make it difficult to gain distance again to continue attacking it.
It is also possible to jump and stand on top of the monster without sustaining any damage during this form, although the player will remain on their location and not be carried along with the monster.