From D&D Wiki
Death's Scythe is a not a weapon for the faint of heart. You have to become one with the weapon to even scratch the surface of it's power. It requires a ten day atunement from a Death Cleric, because when not being wielded by a Death Cleric, you have to, at the start of every turn, make a DC 20 Wisdom saving throw, or be possessed by a demon. Because of it's closeness to death, you can sense when anyone is under 10 HP. Also, this weapon can cast the spell banishment three times per long rest. The damage for this weapon is 2D12+3D4 necrotic damage. This weapon cannot be destroyed by anyone except for the wielder if they willingly choose to throw it in a pool of purity, which can be made by touching the horn of a unicorn to a body of water big enough for a man.