If the head is destroyed first, Mr. Maw becomes a Pacer; if the body is killed first, he becomes a Maw. It also seems to be possible to shoot a Mr. Maw in the neck while its head is extended to split it into both a Pacer and a Maw.
Occasionally, Mr. Maw will split into both a Pacer and a Maw, without any interference by Isaac.
- Rarely, Mr. Maw can spawn with an Eternal Fly. The fly seems to follow the head, and will only turn into an Attack Fly when the head is killed. This glitch occurs if a Psychic Maw attempts to spawn as the head of a Mr. Maw.
- Sometimes, a graphical glitch can occur where Mr. Maw's head, when launched at the player, will have the sprite and behavior of the body. (Pictured above) This is extremely common when using the item Mom's Contacts. Then, if you destroy the actual body part first, the bugged body "head" will shoot at you and become invisible.
- In addition, there is a rare graphical glitch where the head or body can become invisible to the player after a "normal" seperation. If this occurs, the best way of defeating the remaning half is to aim your shots at the blood trail it leaves behind, if the body is left, or to fire back at where the shots originate from, if the head remains.
- Another glitch that can happen is when Mr. Maw launches his head at you it'll go farther than possible, after a while it'll retract back but instead of re-attaching it'll start going back out again. After a while, it will glitch out, with it's head flashing between two corners of a room (Picture above). If the body is killed the head will be stuck in a wall making it impossible to leave the room without a teleport.