When making traps, it’s good to throw the players a curve ball every now and then; it keeps them on their toes.
This isn’t a specific trap. Rather, the dungeon/cave/castle/ whatever that your players are exploring is trapped with several incorporeal traps. Feel free to use any of the traps on this site.
All the traps have full effect on the players. However, when disarming the traps, there is a 50% chance that their attempts just “pass through” the trap. The players may then think it is an illusion or something else. Let them, and let the trap go off.
If you want to have even more fun, only make some of the traps incorporeal. Sit back and enjoy the spectacle as every door, every chest, and every corner of the dungeon is checked, double-checked and disarmed – twice. Throw in some illusions and you’ve got yourself some good fun.