You gain a +2 bonus to attack and damage rolls made with this weapon. The weapon appears to be a mace of disruption, and an identify spell reveals it to be such. The first time you use this weapon to kill a creature that has an Intelligence score of 5 or higher, you begin having nightmares and disturbing visions that disrupt your rest. Each time you complete a long rest, you must make a Wisdom saving throw. The DC equals 10 + the total number of creatures with Intelligence 5 or higher that you've reduced to 0 hit points with this weapon. On a failure, you gain no benefits from that long rest, and you gain one level of exhaustion.