Arcanum of Blood

Magi studying the Arcanum of Blood have focused their studies on the deeper mysteries of the body, their own and others'. The dedicate themselves body and soul to the pursuit of understanding, but most especially body. They have an unsavory reputation as graverobbers and are (incorrectly) associated with the undead, but they are fundamentally most interested in their own bodies, and how to better utilize them as part of their magic.

Blood Arcanum Spells

Level Spells
3rd cure wounds, inflict wounds
5th alter self, enlarge/reduce
9th aura of vitality, vampiric touch
13th polymorph, stoneskin
17th contagion, enervation

Harnessed Blood

When you first focus your studies on Blood, you gain access to a new well of power, in your own blood. When any ability requires you to spend points from your arcane pool, you can replace any number of those points with your own blood by expending hit dice. For each arcane point replaced, roll the corresponding hit die and add your Constitution modifier - your maximum hit points are reduced by that amount. If this process brings your hit point maximum below your current hit points, convert the excess into temporary hit points which you gain.

If you reduce your hit point maximum to zero in this way it is instead reduced to 1, your hit points are reduced to zero, and you lose the ability to spend hit dice in this way until you complete a long rest. As you spend blood in this way, you become paler and more sickly looking - when they are all spent, you look much like a fresh corpse.

Vital Soul

Also at 3rd level, you gain the ability to aid your allies - once during your turn, as a bonus action, you can pay up to three arcane points to temporarily heal nearby allies by touching them. The effect depends on how many points you spend:

For each point spent from your hit dice instead of your arcane pool, you may choose one target of the ability to regain hit points instead of gaining temporary hit points.

Blood Transference

When you reach 6th level, you learn to use your blood as a conduit - you may apply your blood to an ally as an action; it is automatically applied to any enemy that deals damage to you (even if only temporary hit points are lost). This blood is still part of your body, and you can cast spells with a range of 'touch' from up to 30 feet away on targets so marked. This mark lasts until worn or washed away.

You know the locations of all creatures that you have marked within the last day, as long as they are within 60 feet of you. If they are within a mile, you know their rough direction.

If you spend a point from your arcane pool when you cast a spell, all creatures marked with your blood have disadvantage on saving throws against that spell, and you have advantage on any attack rolls made against those creatures as part of the spell.

Vampiric Strikes

At 11th level, you may fill your elemental reservoir with blood instead of elemental energy - it deals necrotic damage, marks the recipient with your blood, and gives you temporary hit points equal to the number of dice rolled.

Blood Bond

When you reach 15th level, you gain the ability to bond a willing ally with you by exchanging blood as a 10-minute ritual that you can perform after completing a long rest. You both gain resistance to all damage except psychic damage; whenever either of you takes non-psychic damage, the other takes an equal amount of the same type. When you gain temporary hit points from your Vampiric Strikes feature, your bonded ally receives those temporary hit points as well.