Ya it's not used that often but you can use a trigger_multiple to hit the player who pases through with a SetFogController input followed by the name of the fog controller you want to assign to that player.
Seen on 2fort when the player passes into the basement area:
If this is your first time logging in after the migration (Feb 8, 2022), you must reset your password to log in. Follow this guide if you're having trouble