Probably the goriest part of the movie. You’ll know when it’s about to happen.

Not exactly squashed but one character's head gets severely mutilated by an accident involving a utility pole and another character smashes his head on a desk repeatedly.

Episode 9 - During the game many people fall from a very high type of bridge and a close up of a woman's skull/brain is shown for a few seconds

Oberyn Martell's head is crushed by the Mountain.

A car runs over a man's head as he lies in the road. Only the characters in the car's reactions are shown (they don't see what happened and assume it's a speed bump), but the noise is quite graphic.

The back of someone's head is hit/smashed with a large rock; I would not describe it as "squashed". The victim survives. We see the rock come down, and blood, but we don't see the injury directly.

Pennywise manipulates their body throughout, including squishing their head flat. Twoards the end their head also deflates like a baloon.

Two heroic characters are seen having their heads bashed in with a baseball bat. The scene is gory and disturbing

Two characters in chapter 3 die from their heads being smashed with a hammer/mallet. The scenes are bloody, but their heads aren't mutilated.

Someone's head get bashed in, it's off camera but there is blood spatter

A character is crushed to death.

One character had his head bashed in by a metal ball, although I don't think there was any gore shown, only blood.

A lot! SPOILERS - mostly happens in the first 15 minutes or so on the beach. To start the fight on the beach Pete Davidson/Blackguard is shot in the head and his face explodes. This happens very suddenly. There is a shot of the corpse later. A soldier on the beach has their head sliced in half by a boomerang. Michael Rooker/Savant's head is detonated by a bomb. Later, a Starro victim is shown in the lab without the star and their face has been melted away.

Someone's head is crushed with an ATM machine.

Very brief shot, but could be disturbing to some. A character's skull implodes, and blood can be seen dripping from their nose and eyes

"ava" from season 3 got her head squashed by a pillar or something on the dock in the ferry boat crash

This happens multiple times, to multiple characters, in multiple episodes, in gory detail.

Not so much squashed. More beaten against a wall.

Tatum gets her neck crushed when being lifted by the garage door and Stu gets his head crushed by a TV.

Mina’s head is crushed during the attack on Trost in season 1. Zofia is crushed by a rock during the massacre of Liberio. Udo is trampled to death by a panicked crowd during the same event. MANGA SPOILERS: During the Rumbling, many people are crushed to death, and a child's head is graphically squashed.

There's a very graphic scene where a man squashes his wife's head in with his bare hands.

EP 7, 19:40 SPOILER ALERT A head explodes. There's blood and they show the body fallen without head and people dirty around them.

At the end by Adam

Yes, notably most often in Black Space. One of the characters continously dies here, several of these deaths involving head trauma. They're pixelated though, and not especially graphic.

Head trauma during car accident

(SPOILER) The killer pushes Kate down and slides her headfirst through some sort of large meat grinder/bread slicer. It’s extremely graphic, so if this triggers you, look away when Kate is pushed onto the table by the killer. Moments later, Simon is killed with an axe through his head, which is also fairly graphic.

Hand man go bye bye

Two, technically. A person's head is repeatedly bashed into a porcelain sink fairly early in the film. This is EXTREMELY graphic and the aftermath is also shown graphically several times. In addition, another character's head is partially split with a cleaver, and while the action of this is offscreen, the character's ghost with the gashed head appears a few times.

lots of episodes have descriptions of violence against other people but the one that sticks out to me for this particular category is mag 80, where a character is beaten to death with a pipe on tape