Bind Blood

You mix your blood with the blood of a willing humanoid with a vascular system, creating a bond between the two of you. Any time you take damage, the target takes half of that damage and you take half. If the target takes damage, it takes half and you take half. Any immunities or resistances you or the target have are negated unless both of you have the same resistances and/or immunities and any vulnerabilities you or the willing target have are negated unless you both have the same vulnerabilities