rare Hellish smite

when you hit a creature with a melee weapon attack, you can deal Necrotic damage to the target, in addition to the weapon's damage. u can use this twice per short rest. The extra damage is 2d8 increasing by 1d8 per 5 lvls(3d8 lvl 5, 4d8 lvl 10, 5d8 lvl 15, 6d8 lvl 20).