Blade of Decay

You can infuse your weapon with necromantic magic that causes your opponent's wounds to fester. As a part of the action used to cast the spell, you must make a melee weapon attack with a weapon against one creature, otherwise the spell fails. On a hit, the target suffers the attack's normal effects. The next time that creature takes damage until the start of your next turn, it takes an additional 1d6 necrotic damage per hit.

At Higher Levels. The spell's damage increases when you reach higher levels. At 5th level, melee attack deals an extra 1d6 necrotic damage to the target damage to the target and the target takes an additional 2d6 necrotic damage. Both die increase 1d6 at 11th and 17th level.