My Jumpeer in Forgotten Realms is gonna go full undead blood magic user(specifically Maho-Tsukai and Akutenshi as they're connected and compliment one another).
This allows him to enhance his spells with blood, letting him substitute material components with blood in the form of HP damage, and lets him freely use Meta Magic by using blood in the form of temporary constitution damage. The users own blood is most effective, but you can use other targets that are willing or restrained.
https://dnd.arkalseif.info/classes/maho-tsukai/index.html
>Maho Metamagic: A maho-tsukai who learns metamagic feats can apply them by paying an additional cost in blood. By draining blood, the maho-tsukai can enhance her spells without using a higher-level spell slot. The cost is a number of points of temporary Constitution damage equal to the level of the metamagic spell. Thus, to cast a vampiric touch spell with the Empower Spell feat applied costs the maho-tsukai 5 points of temporary Constitution damage (3rd-level spell + two levels for Empower Spell). The maho-tsukai cannot enhance a spell to a level higher than he can cast by this means. For example, a maho tsukai must be at least 9th level to cast an Empowered vampiric touch, even though the spell uses only a 3rd-level slot.
The maker seems to have overlooked that undead dont have constitution. so how would you handle this thematically? Should jumper be able to use this anyway, but without cost? With maybe another cost(stamina? higher hp damage?) or just not be able to use it on himself alone, purely needing to use the blood of others? I am not really sure what constitution is supposed to represent in this context, like for the material component part you clearly lose hp bbecause of the blbood loss, but is the constitution loss like an actual sacrifice of life force or maybe just a representation of your health getting worse because of the blood loss?