Blood letter

You touch a nonmagical weapon. Until the spell ends, the next creature hit by the weapon must succeed on a Constitution saving throw or receive a festering wound. A creature with a festering wound takes 2d6 necrotic damage at the beginning of its turn for the remainder of the spell’s duration. A creature can only have one festering wound at a time. Receiving at least 1 point of magical healing closes a festering wound, ending the recurring damage.

At Higher Levels. When you cast this spell using a spell slot of 3rd level or higher, you can increase the damage dealt by a festering wound by 1d6 for each slot level above 2nd.