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.

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.

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.

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.

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

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.

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

Not so much squashed. More beaten against a wall.

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

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.

Someone's head is crushed with an ATM machine.

There is NO literal head squishing in the movie. Thor's head is seized and threatened to be squished, but THAT IS ALL.

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

Mina’s head is crushed during the attack on Trost in season 1. MANGA SPOILERS: Zofia is crushed by a rock during the massacre of Liberio. Udo is trampled to death by a panicked crowd during the same event.

Roanoke

Multiple unnamed enemies are hit in the face with a bat/mallet/gun, and blood splatter is shown, but the aftermath is not visible

A character's face gets bashed in, very graphically!, at the end of the movie.

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

Yes but the camera is on the other character as it’s happening

Hand man go bye bye

Very graphic, the villain steps on a woman's head

Head trauma during car accident