Mr. Maw

Mr. Maw is a monster that can commonly be found in. It is a Maw attached to a Gusher.

Mr. Maw attacks by firing its head towards Isaac. If the Pacer is killed while the Maw is detached, it turns into a normal Maw, and vice versa. Sometimes Mr. Maw randomly separates at will, spawning both a Gusher and a Maw.

Mr. Red Maw
Mr. Red Maw is an enemy added in Booster Pack #5 which acts similarly to Mr. Maw, but has a Red Maw as its head instead of a regular Maw. If the Red Maw segment is killed first, it will release four shots in the cardinal directions like a regular Red Maw. Mr. Red Maw also moves quicker than regular Mr. Maw, ultimately making them a much more dangerous variation.

Swinger
The Swinger is a monster found in Chapter 4. It is a Maw attached to a Globin in its goo form.

Rather than firing its head, the Swinger's head is constantly detached and spins around the Globin clockwise in a fixed radius, while the Globin slowly slides towards the player. The meaty string between the head and body of a Swinger isn't solid and won't hurt Isaac. If the Globin is killed, the spinning head can turn into a normal Maw, and if the Maw is killed, the goo can reform into a normal Globin.

When entering a room, their heads will be retracted, so keep a distance to avoid taking damage once they extend their heads. Since Booster Pack #5, Swingers extend their heads at a much slower pace, making it easier to avoid damage.

Mr. Mine
Mr. Mine is an enemy added in Booster Pack #5 that appears in the Flooded Caves. Mr. Mines are chained to pits and will attempt to launch themselves at Isaac if he comes near. They will occasionally burrow and pop up in another pit, often near Isaac. Upon death, they fire six shots in all directions.

Since pits have a chance to replace rocks in the Flooded Caves where Mr. Mine resides, this can give them more tiles to utilize.

Trivia

 * Though the Maw appears to have eyes when attached to the Globin, if the Maw survives and spawns upon the Swinger's death, then it will have empty eye sockets.
 * Mr. Maw makes Gaper noises while chasing Isaac, while Mr. Red Maw makes the Maw noise only if the Red Maw segment dies first.
 * Mr. Mine is based on the enemy Crunch from The End is Nigh.