A crush is a very uncommon method of being KOed, which involves the player's character being stuck between two solid platforms that move into each other; if the player is unable to move out of the way from the common collision point of the two platforms, then they will be crushed when the two platforms meet. This results in an instant KO regardless of the player's accumulated damage. The effect of crushing is caused by a special hitbox generated on the stage, and as such will not occur in Stage Builder, and can be prevented using the Super Star item.
Stages that can crush
In Midgar, summoning Odin via Summon Materia on the stage will cause him to slice the stage in half. After some time, the two halves of the stage will come back together; players caught in between these two halves will be crushed.
On Distant Planet, when the Red Bulborb swallows a fighter, they will be crushed when its mouth closes. This did not occur in Brawl, where instead the fighter would be trapped and carried offscreen to their death.
In the Subspace Emissary
Outside of the above, Brawl's Subspace Emissary features several levels with crushes in them; owing to the mode's focus on platforming, the player is tasked with correctly timing their movements as to avoid these crushes. The following stages have crushes: