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. This school of magic is closely tied to the Necromancy school, but focuses on redirecting the way necromantic magic afffects the blood within a creature's boy, rather than their life force.

Blood Weapon

At level 2, when choosing this subclass, you learn to link your blood to the magic flow of the Weave.
You can use a bonus action to create a blade made with your blood in one of your free hands, your Blood Weapon. It counts as a magic simple weapon which you are proficient with, deals 1d6 slashing damage on a hit, and uses your Intelligence modifier for attack and damage rolls.
The weapon can also be used as an spellcasting focus for your Wizard spells. While you're not holding it, your Blood Weapon floats harmlessly a few inches away from you.

The weapon lasts for a number of turns equal to your Constitution modifier + your Intelligence modifier, and dissapears if you go unconscious or create another Blood Weapon.
The damage of your Blood Weapon increases to one die higher at levels 6 (1d8), 10 (1d10) and 14 (1d12).

When creating your Blood Weapon, you take necrotic damage equal to one die lower than the damage die of your Blood Weapon (1d4 at level 2, 1d6 at level 6, 1d8 at level 10 and 1d10 at level 14). This damage cannot be prevented or reduced, and bypasses temporary hit points.

You also adquire proficiency in Constitution saving throws, and the Tough feat (if your table doesn't use the Feat optional rules, consider it as a plain increase in 2 Hit Points per level).

Blood Armor

Also at level 2, you undergo necromantic rituals that allow your body to whistand the immense toll this branch of magic will have on it.
While you're not wearing armor or using a shield, are conscious, and are not under the effects of the Mage Armor or Barkskin spells, your AC equals 8 + your Constitution modifier + your Intelligence modifier.
Undead, constructs and creatures with no blood cannot benefit from this feature.

Exanguinate

At level 6, your continued ritualistic efforts have yielded results in manipulating your own blood and others'. You learn the Life Transference and Vampiric Touch spells, which are always prepared and don't count against the number of spells you can prepare.

When you hit a creature within 5 feet of you with an attack of your Blood Weapon, you can use a reaction to cast an altered form of the spells:

• Vampiric Touch: the triggering hit, as well as subsequent attacks of the spell while you maintain concentration, can be done as part of a weapon attack with your Blood Weapon (but no more than once per turn).

• Life Transference: You can force the creature to be the origin of the spell, instead of yourself. The spell fails and the spell slot and use of the ability are wasted if the creature is an undead, construct, or doesn't have blood.

When casted this way, the spell is casted on their lowest level and spends a level 3 spell slot, as normal. Once you cast the altered form of one of these spells, you cannot use it again for that spell until you complete a long rest.

Magic Blood

Starting from level 10, your research allows you to understand how to use your blood as a catalyst to empower your magic effects.
You add your Intelligence modifier to Constitution saving throws made to maintain concentration on a spell, and add your Constitution modifier to Intelligence ability checks (except from History, Investigation, Nature and Religion).

You also learn the Booming Blade or Green-Flame Blade cantrip (your choice). When you use your Blood Weapon to cast them, you ignore the cost of the material components.

If your Blood Armor and Blood Weapon are active simultaneously, you gain a bonus of +2 to your AC.

Weave Veins

At 14th level, your dedication to blood magic has pushed your body past any normal limits of mortal endurance. The very essence of the Weave flows through your veins.
Your current and maximum Constitution score increase by 2.

Once before a long rest, you can attempt to concentrate in two spells simultaneouly, provided both spells are of the 5th level or lower, aren't multiple castings of the same spell, and are of the same school.
When you cast the second spell, make an Intelligence (Arcana) check, with DC equal to 16 + the combined level of the spells. On a success, you take 2d4 psychic and 2d4 necrotic damage, which cannot be prevented or reduced, and ignores temporary hit points; then you must succeed on a saving throw to maintain concentration, with DC equal to 8 + the damage taken. On a success, you can maintain concentration on both spells.
If you fail the initial concentration saving throw, lose concentration, or one of the spells ends, both spells end, and you suffer one level of Exhaustion.