Crushers are sectors in which the floor raises to the ceiling, the ceiling lowers to the floor, or both at once. There are several types of standard crushers. The naming convention used for the crushing specials will generally use "MoveAndCrush" if the crusher stops moving once the floor and the ceiling have connected, but "CrushAndMove" for continuous movement where the crusher moves back away then starts crushing again.
The "Dist" suffix indicates that a crushing special will not move all the way to connect the plane. The original Doom, Heretic, and Strife crushing ceilings generally stopped eight map units above the floor, since moving all the way to the floor also pushes the player's camera below the floor, usually resulting in glitchy visuals.
The "Silent" or "Sil" suffix indicates that the sound sequence used for the crusher's movement will be CeilingSemiSilent instead of CeilingNormal. The two Generic_Crushers allow to optionally use the Silence sequence.
The "A" suffix indicates that a crushing special uses different speeds for upward and downward movement. The crushing mode will also influence crushing speed when encountering an obstacle. In the so-called "Hexen mode", the crusher stops moving as long as the obstacle remains, whereas in "Doom mode" it continues in two different possible ways: a "regular" crusher (upward and downward speeds are both 16) will have its speed reduced to 2; any other configuration will leave the speed unchanged.
Crushing ceilings can be created with the following specials:
They can be halted with Ceiling_CrushStop.
Crushing floors can be created with the following specials:
They can be halted with Floor_CrushStop.
To crush with both floor and ceiling together, use Pillar_BuildAndCrush.
Like vertical doors, a crusher will turn corpses in its path into gibs, unless the corpse actor has a specific Crush state. Alternatively, the DONTGIB flag will entirely prevent crushing the corpse. ZDoom normally replaces the corpse by a different actor, preventing resurrection by arch-viles and similar monsters; however there is the compat_corpsegibs compatibility option to instead set them in the generic crush state, allowing resurrection. The ghost monster bug, however, is only allowed on selected maps where it is known to be part of intended gameplay.
Polyobjects can be used to create horizontal versions of crushers. However, whether polyobject movement causes crushing damage or not depends on the polyobject type, rather than the special used to move it.