Yamato

Transmutation Casting Time: 1 Action Range: Self Components: V, S, M (a small piece of dark cloth) Duration: Instantaneous Description: You weave shadowy energy around your weapon, enhancing your next melee attack. Make a melee weapon attack. On a hit, the target takes the normal weapon damage plus an additional 1d12 necrotic damage as the shadows sap their vitality. The target must also succeed on a Constitution saving throw or have its hit point maximum reduced by an amount equal to the necrotic damage taken until it completes a long rest. This spell's necrotic damage increases by 1d12 when you reach 5th level (2d12), 11th level (3d12), and 17th level (4d12).