Blood Magic Sorcerer

The goal for this was to use the theme of pulling magic out of blood to increase the power of the casters inherent spell casting. Much like cultists use sacrifice to cast spells beyond an individuals power, or to increase the efficacy of a spell, this sub class is built to play as a sorcerer at heart, with all of its base functions left largely alone, but with the flavor of blood magic added on and not as a replacement.

This does not include blood magic in the sense of blood and bone themed spells, but rather blood as a amplifying source of power. 

This does not include blood curses or other blood-as-a-resource mechanics.

Empowered by Blood

Using your own blood you can empower your spell casting. When you cast a spell of first level or higher, you may take choose to take 1d6 necrotic damage per level of the spell cast to increase effective level of the spell's casting by 1. At 9th level you can use your Empowered by Blood feature to increase the casting of any spell of 1st level or higher by 2

Blood Component

Blood from living creatures, including yourself, can be used as an active component in any spell that you cast. A small amount of blood can replace most material components, and larger volumes can be used instead of costly components for spells that require consumption of components. For instance sacrifice of an amount of blood in a medium creature could replace one hundred gold worth of material components such as diamonds. The value of any amount of blood is determined by volume, quality, freshness, and origin. An ounce of goat blood is nowhere near as valuable as an ounce of humanoid blood. The same comparison hold true for humanoid to celestial/fiendish blood, or to divine or similar. Ultimately, value is determined by the DM within loose but reasonable consideration.

Blood Channelling

You have experimented enough with blood magic to have inured yourself to its worsts side effects. You gain resistance to necrotic damage, including that of the Empowered by Blood feature. Additionally, you no longer need to use your blood alone for your Empowered by Blood feature. When you cast a spell and would take necrotic damage to Empower it, any willing creature within 30 feet of you can take any portion of the resulting necrotic damage instead of you, as their blood is siphoned toward you to fuel the invocation. This relieves some of the strain on you, and you must only take any necrotic damage that is left over as a result of this feature.

Willful Blood Channeling

So great has your knowledge of Blood magic become, and your power over it, that you can siphon the required blood for the Empowered by Blood feature from unwilling creatures. A number of creatures up to your spell casting ability modifier (minimum of 1) within 30 feet of you that you can see that are unwilling to contribute must make a Constitution saving throw against your Spell Save DC. On a successful save a creature takes no damage, and you must take their share of any resulting necrotic damage. On a failed save a creature takes a equal share of the resulting necrotic damage dealt. 

Font of Blood Magic

Your ability to empower and manipulate the magical energy within blood is nearly boundless. As a bonus action, you can call forth the magic within your blood, changing it into a Font of Blood magic energy. Any number of creatures you choose that you can see withing range must make a Constitution Saving throw against your spell save DC. On a successful save, the creature suffers no ill effect. On a failed save the creature is Blood Cursed. Blood Cursed creatures have vulnerability to necrotic damage, and automatically fail Constitution saving throws against Willful Blood Channeling for the duration of your Font of Blood Magic. Furthermore if any creature is killed by the necrotic damage from Willful Blood Channeling, you regain half of the necrotic damage dealt back as HP, and regain a spell slot equal to 1/3 the creatures CR rounded down, as their blood is added to your Font of Blood Magic. Thus a creature with a CR less and 3 regenerates no spell slots, as their blood is too inferior to fuel your Font of Blood Magic's power. This effect lasts 1 minute, or until you dismiss it as a bonus action. Once you use this feature you can't use it again until you finish a long rest.