Weapon (longsword), very rare
This brutal longsword is embedded with a rotating chain of jagged blades, capable of tearing through armor and flesh. You gain a +2 bonus to attack and damage rolls made with this weapon.
On a hit, you can activate the rotating chainblades. The target must make a Constitution saving throw (DC = 8 + your attack bonus) or take 3d6 slashing damage and suffer deep lacerations, causing them to take 2 additional slashing damage from all incoming attacks for 1 minute. On a successful save, they take half damage and suffer no additional effects.
Once the chainblades are activated, they cannot be activated again until you take a short rest. To activate the chainblades, the weapon must be wielded with two hands.