Blood Fueling (Homebrew)

Your body chemistry alters to allow you to heal from blood you have collected from other sources. If a creature fell to 0 hit points within the last minute, you may touch the creature to regain one hit die in the form of a vial of blood.  If you have max hit dice, you may expend any hit dice remaining (above your maximum) to regain health without using the material component. You cannot collect blood from a construct, elemental, plant, or undead, or a creature you have gathered blood from since your last long rest. The creature must be of CR 1 or higher to collect hit dice.

As you level, this spell effects creatures of lower CR, and grants extra hit dice from creatures whose CR is higher than your level. When you reach 5th level (CR 1/2; and 2 hit dice per higher CR creature), 11th level (CR 1/4; and 3 hit dice per higher CR creature), and 17th level (CR 1/8; and 4 hit dice per higher CR creature).