Crush
When ending a flying or jumping movement, the creature can land on targets that are at least three size categories smaller than itself. Targets can make a Reflex save (DC 10 + half the creature's CR + the creature's Strength modifier). Targets who succeed take half the listed damage and move to the closest open square (this movement does not provoke attacks opportunity). Targets who fail are knocked prone, take the listed damage, and are pinned. Each crushed target can attempt to escape the pin normally on its turn, and the pin ends automatically if the crushing creature moves off the target’s square. A crushed target does not take damage from the crush more than once, unless the crushing creature moves fully off that creature and then back onto it.
Source
Alien Archive pg. 153