Thoughts on creating a Spellcaster that uses hit points for spell casting instead of spell slots.
I was just wondering about home-brewing a walock NPC who’s patron saps hitpoints in exchange for spell casting. Essentially, as long as the character has hitpoints they can cast as many spells as they like but with each one it takes a toll.
Balance is obviously an issue here in preventing them from just being healed by the party and used as a spell battery in exchange for healing but Im thinking perhaps balancing that out by making con saves to prevent them from passing out from blood loss or something from wounds appearing on their body as till for the spells. Aswell as that, spells would have different hit point costs that scale with levels like a first level costing 5, 2nd 10 and so on.
Backstory and lore could be pretty interesting as to how they received their patronage, why they took such a harmful deal, they could be good or evil depending on their motives for doing so and other fun stuff!
Let me know what you think or if you have any ideas!
Assuming we are talking about D&D 5e, you should know that using hitpoints to extend spellcasting like that is fundamentally opposed to the way that 5e is designed and balanced. You’re getting into very dangerous homebrew territory when you start breaking the core design of the game like that. It’s akin to homebrewing a spellcaster that gets access to 4th level spells at level 2. The game just isn’t designed with that in mind.
Of course, none of that matters if you are homebrewing an NPC who will just be around for one fight as a bad guy. But it sounds like the NPC is intended to travel with the party based on your wording, which means you need to consider them like you would a PC.
Also, be wary of creating a DMPC. Your job as the DM is not to put someone in the party who can do cool stuff, it’s to let the players do cool stuff in the environments you create.
Consider instead that “blood magic” could be handled as a pure flavour thing, where you describe each spell as your NPC cutting into himself and drawing out the magic. It just becomes his version of somatic components.