Blood Magic

Blood magic is, as the name implies, a form of magic based around manipulation of blood. It uses the mana of one's vitae to cast and empower spells. 

Hemophilic Blade

Beginning when you select this subclass at 2nd level, you acquire the training necessary to effectively arm yourself for battle. You gain proficiency with light armor and martial weapons.

Additionally, you gain the ability to channel magical energy into a weapon of your choice, turning it into a hemophilic blade. Whenever you finish a long rest, you can touch one weapon that you are proficient with and that lacks the two-handed property. When you attack with this weapon, you can use your Intelligence modifier, instead of Strength or Dexterity, for the attack and damage rolls. You can magically summon this weapon to your hand as a bonus action. This weapon can be used as a spellcasting focus. This benefit lasts until you finish a long rest. Any weapon that you enchant or summon with your spells can also be treated as a hemophilic blade, for the duration of the spell.

Bloodcasting

At 2nd level, you gain the ability to convert your life energy into magic, and vice versa. When casting a spell while holding your hemophilic blade, rather than using a spellslot, you can choose to cast the spell using your health as a resource, taking damage of your hemophilic blade type equal to 1d6 per the spell's level. This effect deals half damage, rounded down, if you have temporary hit points. You can only cast spells of 5th level or lower in this manner. You can cast spells in this way a number of times equal to 1 + your Intelligence modifier (minimum of 2). You gain an additional use of this ability at 6th, 10th, and 14th level. You regain expended uses of this ability on a long rest.

When you use this feature to cast a spell that affects your AC in some way, such as mage armor or shield, you gain an additional bonus to your AC equal to half your Intelligence modifier (rounded down) for the duration of the spell.

Vascular Assault

At 6th level, you become much more adept with your hemophilic blade. You can attack twice, instead of once, when you take the attack action with your hemophilic blade. Additionally, if you use your action to cast a cantrip, you can make an attack with your hemophilic blade as a bonus action.

Vampiric Thirst

At 6th level, your hemophilic blade scores a critical hit on a roll of 19 or 20. Additionally, whenever you score a critical hit with your hemophilic blade, you gain temporary hit points equal to the damage dealt.

Sanguine Shield

At 10th level, your blood magic gains much stronger defensive properties. While you have temporary hit points granted to you by your hemophilic weapon or spells casted with blood magic, you have resistance to all types of damage.

Greater Blood Arcana

Starting at 14th level, you've mastered the art of blood magic. You can use blood magic to greatly empower one damage-dealing spell. When you empower a spell in this way, you take irresistible damage equal to 1d8 per the spell's level, and it gains the following properties:

• Saving throws made against the spell are made with disadvantage.
• Any and all spell attack rolls are made with advantage.
• Targets that are immune to the spell's damage type are treated as if they had resistance instead.
• Targets affected by this spell have disadvantage on attack rolls until the beginning of your next turn.

Once you empower a spell in this way, you cannot do so again until you complete a long rest.

Additionally, your hemophilic blade scores a critical hit on a roll of 18-20.