An item with random effect could be nice. With good effects, bad effects and misc effect.
Only one effect on the list can apply

Good Effect :
- All party gain atk +30% and damage taken -40%
- Expérience point double for the current floor
- Change all the party into a random monster
- Every monster in the current floor change into monster lvl 1.

Bad Effect :
- One monster is changed into a manticore (It can kill a player with a single shot)
- Traps are boost to Floor Traps for the current floor (if someone take a trap, every player in the floor will take the effect).
- All monster gain atk +30% and damage taken -40% on the current floor
- Apply paralysis on all party for the currect floor

Misc Effect :
- All traps are changed in chest and all chest are changed in trap
- Teleport the party on the previous floor, or on the next floor
- Open a gate that summon a monster every 10 seconds. (the gate can be kill to stop the monster's summoning.