Blood Bond

You weave the fates of two creatures together through the power of blood. Using a sharp implement coated in a creature's blood, make a melee spell attack against another creature of your choice that you can reach. On a hit, the creature makes a Constitution saving throw, and on a failed save, the target is bonded to the creature whose blood was on the implement used to cast the spell until the spell ends. This spell has no effect on creatures that do not possess or require blood.
While the two bonded creatures are within 60 feet of one another, the target takes damage equal to half of all damage it deals to the creature you bonded it to.

At Higher Levels: When you cast this spell using a spell slot of 5th-7th level, the target takes damage equal to the damage it deals to the creature it's bonded to, and the damage taken ignores the target's resistances. When you cast this spell using a spell slot of 8th level or higher, the target takes damage equal to twice the damage it deals to the creature it's bonded to, and the damage taken ignores the target's resistances and immunities.