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.

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.

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

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

Oberyn Martell's head is crushed by the Mountain.

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

Not so much squashed. More beaten against a wall.

There's a fair amount of decapitation which leads to heads being kicked and carried around

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

A character is crushed to death.

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

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

Does a head getting eaten count as squashed? I'd say yeah, but some my disagree.

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

Roanoke

Twice throughout the movie a head is squashed, one being possibly the most gory death in the franchise.

Someone's head is crushed with an ATM machine.

Heads explode in the game from direct gunfire and other assaults.

A head is run over by a lawn mower and is shown again stitched back together

In the first episode of Golden Wind Giorno uses one of his abilities to send the damage from an attack back to his attacker, Leaky Eye Luca. This causes the back of his head to cave in with an imprint of the shovel he was attacking Giorno with.

Several heads /are/ blown off by a gun, though

Hand man go bye bye

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

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.

Deputy gets his head squished by gator while being chomped on

Not on screen, but people are shown with severe head injuries

Someone's head gets Cronched!

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