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 
Silver Buttons. 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 Silver Buttons.
Notes
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 Silver Buttons.
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 Silver Buttons, 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 Silver Buttons, 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 only in 
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 Silver Buttons, 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.
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 several 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 Silver Buttons.
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).
Notes
- 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.
- With
- Fire Mind tears that hit these monsters can still cause explosions.
- Hitting Grimaces increases the Dead Eye damage multiplier.
- Grimaces can appear in rooms with Silver Buttons, and will stop shooting once all buttons are pressed.
- 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.
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.
- Previously, Broken Gaping Maws were extremely hard to find. As of Booster Pack #5, they are now more common to find in rooms.
- 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. They now can be found surrounded by spikes.
- 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.
Stone Grimaces and their variants play their appearance animation for a second before resuming as deactivated in a cleared room if they were deactivated.
 The Binding of Isaac: Rebirth
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