Bludgeon of Nightmares

Weapon (flail, mace, or morningstar), rare (requires attunement)

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. Curse. This weapon is cursed. Becoming attuned to it extends the curse to you. As long as you remain cursed, you are unwilling to part with the weapon, keeping it on your person at all times. While attuned to this weapon, you have disadvantage on attack rolls made with weapons other than this one.

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.