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!
Simple solution is "resistant damage" - damage taken by burning your life force to power spells can only be healed by natural healing, not magical healing. It's tracked separately, and similar to subdual damage, you add it together with normal damage to determine if the character reaches 0HP. If you choose to go this route, I suggest that HP not be your primary fuel for spellcasting, but rather have the patron grant a class feature that allows "overcasting" by burning one's life force to power additional spells after you've run out of normal spell slots.