Ancient, forbidden magics. When casting spells causes physical hurt on the spellcaster, then it is an art reserved to only the toughest, and most ruthless of barbarians. Blood magic as depicted here is not necessarily evil – for example, it might be a cultural tradition, or a representation of how you re-shape the world through strong emotions. Like a really, really bulky bard.
A warlock-based 3rd-caster. This subclass will be reminiscent in many ways to the Eldritch Knight and Arcane Trickster, though it uses hit die instead of spell slots, and learns spells from the Warlock spell list instead of the Wizard’s. For most of your adventure, you will only be able to cast spells while raging, but in exchange, you get to learn spells from all schools of magic instead of just two!
Want to check it out? Here it is: https://www.dmsguild.com/product/373187/Barbarian–Path-of-Blood-Magic
Trekiros 