If the head is destroyed first, Mr. Maw becomes a Pacer or Gusher; if the body is killed first, it 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 (or Gusher) and a Maw, without any interference by Isaac.
Mr. Maw will sometimes spawn with an Eternal Fly surrounding it.
The head and the body will automatically detach after a certain period of time (varies from almost instant to half a minute). Once it's detached, it always spawns an Eternal Gusher and an Eternal Maw.
For the variant that would spawns an Eternal Fly, it will spawn 3 Eternal Flies surrounding itself.
- 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 (as pictured from the right). This is extremely common when using the item Mom's Contacts. Then, if Isaac destroy the actual body part first, the bugged body "head" will shoot at Isaac 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" separation. If this occurs, the best way of defeating the remaining half is to aim Isaac's 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 Isaac 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.