??? is a monster found in the Secret Lab, an area accessed after winning the Defend Mission. There are 10 different monsters with the same name, they are separated by 3 groups, one's give 45000 EXP, other 47500 EXP and other 50000 EXP with exception of one giving 42500 EXP.
Like rest of the Defend Mission monsters, damage from all weapons are severely reduced, except for the Special Wand.