The Blood Mage has learned to turn their flesh, and even their own life force, into fuel for their spells.  Due to the physically taxing Nature of Blood Magic, a wizard looking to practice this art must undergo multiple rituals, which physically alters the way they think about and cast spells.

Written in Blood

At level 2, when choosing this subclass you learn to internalize your knowledge of the Arcane.  You learn to record your spells using your own body as a backup spell book, known as a Body Template.  You can preform a ritual in which you record spells you already know into your Body Template for a cost of 10GP,  and 1 hour per level of spell.  Constitution becomes your spellcasting ability.

Bloody Evolution

In preparation for the immense toll this branch of magic will take on the wizards body, they undergo rituals that alter their body in the following ways. They gain and additional +1HP per wizard level.  You gain advantage on Death Saving Throws.  Lastly, a number of times per day equal to half your proficiency modifier rounded up, during a short rest, you can reroll a total number of hit dice equal 1 plus to your Constitution modifier and choose which roll to keep.

Blood Sacrifice

At 6th level you've learned ways to alter the Weave, for the price of your own life's blood. 

You have a pool of D12's equaling 1 plus your combined Proficiency modifier + your Constitution modifier.  During the casting of a spell you may spend up to your spell casting modifier in Blood Sacrifice dice to affect your spells in a number of ways.  You pick two of the Blood Magics options available now, and two additional options at levels 10 and 14.  At level 10 and 14 you may replace your chosen Blood Magics  You may choose multiple effects to apply to the same spell, stating which effect receives which dice, but the total number of dice per turn does not change. 

For example:   If you had an intelligence of 16 you could use 3 Blood sacrifice dice per turn.  If you launched a fireball that engulfed an enemy and an ally you could use 1 die for Blood Clotting to give the enemy disadvantage on the save, 1 die for Blood Poisoning to deal additional damage to the enemy, and 1 die for Blood Letting to protect you ally from the spell.

Whatever number of dice rolled, you take the total number rolled from all of the dice spent that turn in damage, directly to your normal Hit Points, bypassing any Temporary Hit Points.  This damage can not be reduced by any means.  These dice are restored after a long rest. 

You also learn the false life spell. It's always prepares, doesn't count against the number of spells known, and can be cast at 1st level at will.

Adrenaline Cycle

Spend 2 Blood Sacrifice die to gain an additional reaction

Anemia

This feature activates whenever a Blood Sacrifice is made. In addition to the spells normal affects, you may inflict the poison status affect on any creatures affected by your spell, up to the number of blood sacrifice die spent.  The affect lasts until the start of your next turn.

Aneurysm

Give a number of creatures equal to the number of dice rolled disadvantage on the spells saving throw.

Blood Letting

Choose an number of Blood Sacrifice die, and an equal number of creatures are unaffected by the spell.

Blood Transfusion

You may increase the Level of the spell by up to half your proficiency modifier, for 2 dice per level.

Hemophobia

For your sacrifice, you learn to overcome even the most resilient of your enemies defenses.  You may spend up to 4 Blood Sacrifice die to reduce an enemies defenses against your spell. Example: An enemy who had an Immunity.  1 die would lower Immunity->Resistance, or Resistance->Normal, and 2 Die will lower Immunity->Normal.  To impose weakness requires a larger sacrifice, 2 Dice for Normal->Weakness.  This reduction last until the end of the Spell or the casters turn, whichever comes first.

Hypercoagulability

Increase the duration of a spells effect by sacrificing your own life force.  For each Blood Sacrifice die spent, double the duration of a spell.

Sanatio Sanguinis

This feature activates when ever a Blood Sacrifice is made.  Pick a number of creatures within 60ft of you, equal to the number of Blood Sacrifice die spent.  You may end any, or all of the following conditions afflicting them: Blinded, Charmed, Deafened, Frightened, Paralyzed, Petrified, Poisoned, or Stunned

Sepsis

Give a number of creatures equal to the number of dice rolled the combined dice roll additional damage, of the spells type.  

Fortified Endurance

At level 10 your continued ritualistic efforts have yielded results in strengthening and manipulating your body.  You gain Immunity to Disease, advantage on saving throws against poison, and you have resistance against poison damage.  You also learn alter self, which you can cast at will, and doesn't count against the number of spells known.

In the Blood

At 14th level your dedication to blood magics have pushed your body past any normal limits of mortal endurance.  When you receive healing from any magical source, you receive the maximum amount possible.  If you start combat without any of your Blood Sacrifice dice, you regain a number equal to one third of your wizard level (rounded down).