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!
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Using hit points as a resource very quickly starts to feel less and less like spending health and more and more like you’re spending your Cleric’s spell slots, which isn’t very fun for your Cleric. It works in some other games but I don’t think I’ve ever seen an effective implementation in D&D.
You could maybe get around the begging-for-healing issue by having spells reduce your max HP instead, but I still doubt it would be balanced, it adds a lot of bookkeeping, and you end up getting constantly oneshotted and begging for healing later anyways.
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.
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.
How about instead of just spending HP, you have spell slots similar to the D&D system. Then, once you run out of slots, you can choose to spend HP and/or roll against CON to cast more spells? That way in a normal situation, the player would cast as per normal and within limits. Once things get tough, they can be pushed to run the risk of casting to exhaustion or unconscious states.
Additionally, it would need to be a holdout/failsafe option, to help with said balance issues. Something along the lines of that CON Save increasing in DC with each successive attempt to cast without slots. A failed save results in a level of Fatigue, lowered Max HP, etc., until they either stop attempting to cast or die from the effects and become a wraith in eternal service to the Patron.
Warlock is required to cast their spells at the highest level. Since this is a warlock patron it probably shouldn’t be allowed to pick and choose which level of spell it can cast. Consider also converting the warlock spell slots it gives into bonus HP to fit the flavor, but probably at a less than 1:1 ratio for what it costs to cast that same spell since they have innate HP and healing.
As you’ve suspected, this is gamebreakingly powerful and absurdly difficult to balance. Every build in the game would benefit from having this ability and would be made stronger by multiclassing into it. Every other warlock would be pointless because choosing another one would lock you out of this patron. Any multiclass caster is an infinite spell slot source by itself.
You could try to balance it by making it once per day, but why? That’s too fair and not the original intent of design, just accept the imbalance it creates and make it fun to use.
You could make it more glass cannony, eg - that hit point loss after casting consecutive spells gets more dangerous and each cast increases a chance for a perils of the warp style head explosion?
GURPS does this, maybe look that and convert
I worked up a custom template for a blood mage based on a homebrew I found and lost long ago. The basis was that the caster used spell slots as usual, but could expend hit dice for additional slots, or to use other class features or even boost some of their spells. It requires careful balancing, but is plenty of fun.
As I implemented it, it laid on top of their normal class, but it wouldn’t be too hard to work it up as it’s own class entirely. As another poster suggested, you could introduce a caveat that any health used to power a work can only be regained through natural means, or is only restored on a long rest, or something to that effect.
