Bloodbound Ritual

You bind your essence to a creature by performing a macabre ritual using its blood. For the duration, whenever you take damage from an attack, spell, or effect, the bonded creature takes half the damage you receive (rounded down). This damage bypasses resistances and immunities.

As part of the spell, you can choose to willingly take up to 10 points of necrotic damage on your turn to force the bonded creature to take half of that damage as well (no saving throw required).

 At Higher Levels. When you cast this spell using a spell slot of 6th level or higher, you can increase the maximum necrotic damage you can willingly take by 5 points per level (e.g., 15 points at 6th level, 20 points at 7th level, etc.).