Stone Grimace
A Stone Grimace is an invincible stationary statue with the shape of a head with a wide-open mouth and hollow eyes. Stone Grimaces will sporadically spit a Red bullet in Isaac's direction until the room is cleared by killing regular enemies, or by pressing 
Pressure Plates. When the room is cleared, the Stone Grimace closes its eyes and mouth.
Variations
Vomit Grimace
The Vomit Grimace fires an explosive 
Ipecac-like shot. Like Stone Grimaces, Vomit Grimaces will stop firing at Isaac when the room is cleared.
Triple Grimace
The Triple Grimace fires a triple shot. Like Stone Grimaces, Triple Grimaces will stop firing at Isaac when the room is cleared.
Gaping Maw
The Gaping Maw sucks Isaac towards it, along with warping Isaac's and any enemies' bullet paths. It does not fire any shots and simply functions as an obstacle, and is often surrounded by spikes. 
They can, however, be deactivated by Pressure Plates.
Notes
- If a Gaping Maw is rerolled with
D10, it will always turn into a 
Broken Gaping Maw.
Broken Gaping Maw
A broken variant of the Gaping Maw. It alternates between active and inactive every four seconds, but it has a much stronger attraction power. Just like regular Gaping Maws, they can be deactivated by Pressure Plates. Prior to Afterbirth+ Booster Pack 5, only one room in the game contained Broken Gaping Maws.
Constant Stone Shooter
Constant Stone Shooters, sometimes referred to as Turret Grimaces, constantly fire bullets in a fixed direction, and do not stop firing even after the room is cleared. The exceptions are rooms with Pressure Plates, which deactivate them once they are all pressed.
Cross Stone Shooter
Cross Stone Shooters were added in Booster Pack #4.
The Cross Stone Shooter, sometimes referred to as Cross Grimace, constantly fires bullets in four directions, alternating between cardinal and diagonal directions. If the room has to be cleared, whether by killing enemies or by pressing Pressure Plates, then Cross Grimaces will deactivate upon the room's completion like a regular Grimace. However, if the room is purely trap based and does not present an objective to complete, then Cross Grimaces will continue shooting indefinitely.
Brimstone Head
Found in 
Gehenna and 
Sheol, the Brimstone Head, sometimes referred to as Brimstone Grimace, periodically shoots 
Brimstone lasers and does not stop firing even after the room is cleared. The exception is pressing all Pressure Plates, which deactivates them.
Stone Eye
The Stone Eye resembles the 
Bloodshot Eye. It constantly rotates in a clockwise circle and shoots a flickering 
Technology laser. It stops firing after the room is cleared. Unlike any other Stone Grimace variants, the Stone Eye appears to despawn when the room is cleared, exited, and then re-entered. 
Stone Eyes will do an entire rotation before shooting their laser.
Bomb Grimace
The Bomb Grimace is a unique Stone Grimace in that its only purpose is to keep a single 
Throwable Bomb spawned. A few seconds after Isaac takes the bomb, it will spawn another.
If it is destroyed with an instant-death attack such as 
Euthanasia or 
Little Horn, it spawns 10 throwable bombs.
Always spawns during the battle of 
Tuff Twins and 
The Shell.
Quake Grimace
The Quake Grimace fires a line of rocks in one direction upon landing every 3 seconds. In most cases, even after the room is cleared of vulnerable enemies, they will continue this behavior. However, they can be deactivated from Pressure Plates.
If a 
Secret Room or a 
Super Secret Room is placed in the path of their attack, the attack will break the wall and open the entrance.
Notes
- These monsters are impassable, even with flight.
- These monsters can be destroyed using
Chaos Card, Little Horn and Euthanasia, though they will respawn upon leaving and re-entering the room they were in. - With
Infestation 2, killing Stone Grimaces creates a Blue Spider, allowing blue spiders to be farmed by leaving and re-entering the room. 
Fire Mind tears that hit these monsters can still cause explosions.- Hitting Grimaces increases the
Dead Eye damage multiplier. - If an uncleared room has Cross Grimaces, leaving and then re-entering the room by bombing a door will make them stop shooting, making the room easier.
- 4 Stone Grimaces can appear in
Loki's boss fight.
Gallery
Sketches of monsters for the Binding of Isaac: Rebirth, including the Stone Eye in the first square of the first row, which was formerly called "360 Stole Laser"; the Constant Stone Shooter in the second square of the first row, which was called "Constant Stone Shot" and the Brimstone Head in the third square of the first row (no visible sketch name).
Trivia
Stone Grimaces and their variants play their appearance animation for a second before resuming as deactivated in a cleared room if they were deactivated.
- They now no longer reuse their appear animation in a cleared room when the player re-enters it.
- If a Constant Stone Shooter is deactivated, it closes its eyes and mouth and stops crying, looking similar to Stone Grimaces upon deactivation. The difference is that deactivated Constant Stone Shooters still have a crack on top of their heads.
- If a Gaping Maw or Broken Gaping Maw is deactivated, unlike other Grimaces, it doesn’t fully close its eyes. Instead, it closes its eyes only partially and makes a frown.
- Grimaces will turn green if poisoned.
-
Great Gideon is the boss variant of Stone Grimaces. - Gaping Maws were going to have fangs, as shown on the Bestiary.
- The Bomb Grimace and Quake Grimace first appeared in the Antibirth mod.
- Quake Grimaces have substantially different designs compared to their original appearance in Antibirth. Most notably, they are the same size as other Stone Grimaces instead of being twice as large, and they do not have the large gash in their body.
- Pre-release content of Repentance as well as the "death preview" shows the original version of Quake Grimaces, suggesting this change was made late in development.
- Bomb Grimaces are the only Grimaces who don't appear in the bestiary.
Bugs
 Bug!
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 Using the D10 in a room with  Stone Grimaces will turn them invisible. They will not fire, but the space they occupied will prevent Isaac from moving through it like an invisible wall.
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 The Binding of Isaac: Rebirth
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