Hemomage

Hemomage's use blood aura's to enhance their spells by using their health instead of spell slots and improving the spells they cast at the cost of their own health and becoming immune towards healing from allies and instead having to fend for themselves by using their blood aura siphon health from others and using improved offensive healing from their blood aura

I... do not know how to make a subclass. I purely made this because normal D&D didn't have a blood mage (surprisingly)

I may or may not have taken a little inspiration from one of the Dragon Age sub-classes which might have been a poor decision but eh, DM approved it, I liked it but screw it I need opinions

Blood Aura

Beginning when you choose this school at level 2 you gain access to the Blood Aura ability and gain an additional 2 health every level as well as gaining proficiency in martial weapons

Blood Aura:

as a bonus action you can choose to activate your Blood Aura and receive the following effects, Blood Aura lasts for 1 minute or until you become unconscious:

- Your spells deal an additional 2+Spell level necrotic damage to enemies

- When casting spells you instead use your health instead of spell slots taking 1d4’s equal to the spells level damage, this damage can be fatal, cantrips are unaffected

- You are unable to use or be healed by conventional healing spells but offensive healing spells (e.g. vampiric touch) are unaffected and heal additional hit points equal to wizard level

- You gain resistance to necrotic damage

- As an action you can siphon the remaining life force of nearby corpses, healing 1d6 for each corpse within 30 ft, can be used once per Blood Aura usage

OR (up to dm)

- As an action, you can target creatures up to your proficiency bonus within 30 ft, forcing them to make a constitution saving throw and dealing 1d6 necrotic damage to each of them or half on a successful save and healing the same amount, can be used once per Blood Aura usage

You can activate Blood Aura an amount of times equal to your PB per short rest and can choose to end Blood Aura at anytime as a bonus action

Vein Sense

Additionally upon choosing this school, you gain the ability to see the blood in most creatures veins, allowing you to easily notice and mend otherwise unnatural blood

- Gain advantage on medicine checks related to a creatures blood (e.g. Poison, Corruption, faster heartbeat, etc)

Life Thief

Upon reaching level 6 you add Life transference into your spell book if you don’t already have it. Additionally while using Blood Aura you can choose to use it in reverse once per blood aura, this does not trigger blood aura’s damage to self.

You siphon the lifeforce from a creature that you can see within 20 ft, that creature must make a constitution saving throw and take 4d8 necrotic damage or half on a successful save, you heal for half the damage the creature took rounded down

Arcane Blood

When you reach level 10 you can use both your health and spell slots for spells

When you cast a spell while Blood Aura is active you can use a spell slot equal to the spells level to enhance the spell making the spell deal additional damage equal to the spells level and giving the targeted creature disadvantage on the saving throw for the spell if it has one

Blood Savant

When you reach level 14 you’ve learned how to use your Blood Aura to its maximum potential

Blood Aura gains the following benefits:

- when a creature dies within 30 feet of you, you heal 1d6 + spellcasting modifier

- you can use Reverse Life Transference on friendly creatures without expending its use during Blood Aura, they can make the constitution saving throw to resist it but can fail it on purpose, you heal equal to the damage dealt. Additionally, using Life Transference normally will not deal Blood Aura's damage to you

- you can choose to resist the damage taken from using your health for spells a number of times equal to half your PB and regain these charges after a short or long rest, this spells level can be no higher than 5 level. This feature can also be used on a normal use of Life Transference with no penalty to the healing

- gain advantage on concentration saving throws while blood aura is active and when below half health, any healing you gain while blood aura is active is doubled