Wiki: trigger_gravity

trigger_gravity - Brush Entity

This entity sets the effect of gravity for any player that touches it. It acts as a multiplier for sv_gravity.

Target (target)
Name (targetname) - Property used to identify entities.
Master (master)
Delay before trigger (delay)
Kill target (killtarget)
Target Path (netname)
Sound style (sounds)
Message (message)
Gravity (gravity) - Gravity multiplier. For example, a value between 0 and 1 is low gravity.

Level of gravity stays set after being put into effect - use two brushes, one with the new gravity, one with the old, to make sure the player returns to normal gravity in situations where that is necessary.
Most keyvalues and all spawnflags have no effect.
This entity cannot be toggled. Triggering it has no effect, neither does having a master.
Contrary to what most FGDs state, the gravity property is not strictly between 0 and 1, it can be any value.
If one of the CLIPHULL textures is used instead of AAATRIGGER, this trigger will only affect standing (CLIPHULL1) or crouching (CLIPHULL3) players.