This thread http://paizo.com/paizo/messageboards/paizoPublishing/pathfinder/pathfinderR PG/houseRules/castFromHitPointsTrope reminded me of a similar spell fuel system I've been brain-storming for a while that doesn't actually use up HP, but works alongside it:
The caster has a Spell Fatigue (spell burn, arcane stress, whatever) value they keep track of alongside their HP.
Every time the character casts a spell, they add 3 x spell level to their Spell Fatigue. Addition being slightly easier than subtraction and all that...
If Spell Fatigue runs higher than the character's current HP, they gain a penalty to all rolls, -1 maybe, possibly -2 since casters are all about trying to avoid damage anyhow.
If Spell Fatigue reaches the character's max HP, they pass out or are incapacitated for about as long as they'd need to regain spell slots. Not sure about if it goes over max hp, whether that would even be possible or if they'd need a concentration check to get that last spell off, etc. DC 10 + however much they go over max HP?
Spell Fatigue resets under the same conditions that a caster would regain their spell slots.
0-level spells could just add 1 to Spell Fatigue.
Anyhow, I haven't had a chance to try any of this out. Any thoughts?
All casters are based on con now, huh?
Umbra, no, this is just a brain-storm of an idea inspired by people thinking along the lines of HP-fueled spells. I don't really like the idea of weighting CON that much for casters either, but I like to play around with the rules enough that I think just about anything is worth some theoretical tinkering. I admit I wouldn't want to use what I'm describing in-game in its present form, maybe never.
I suppose you could give them a mental HP based on WIS or INt or whatever, if HP is d6, give them d12 MHP, d8 HP - d10 MHP; something like that. Allow spells to optionally target MHP and maybe melee fighters could make "feint" attacks that damage MHP. Stupid idea? Maybe. Five minutes of thought? Definitely. As a fix, it's also really going off on a tangent and adding a lot of math I was meaning to subtract (no pun in...well maybe I'll say I did; that's actually vaguely clever now that I look at it.)
Holy 15 minute adventuring day!
Based on what you've described, a caster whose Spell Fatigue reaches their max hit points has to sleep for at least 8 hours. The problem is "under the same conditions a caster would regain their spell slots" means it only resets once per day. So if the caster novas in the morning he is out until the next day.
Have you considered having Spell Fatigue heal at the same rate as nonlethal damage (1 point per hour per character level)?
Yeah, I wasn't even thinking about non-lethal heal rates, that makes some sense...it does seem a bit fast to be re-gaining spell use though and pretty much doubles the amount of number tracking.
How about, if you stay under your max threshold, you're just tapped out until you can rest, as per usual. If you burn your fatigue over that threshold, then you take twenty on a sack of potatoes check for a while until level per hour heal rate brings you back down to max? Just how far over the max threshold you can go could also be determined by an ability score or modifier. I do like the idea of the wizard konking out when they burn more juice than they're supposed to, that's pretty classic.
Why not just keep them unlimited like they are currently?
0-level spells could just add 1 to Spell Fatigue.
Eheh hehe. I thought of that when I was typing this up, but I had one of those moments where I couldn't remember if it was an actual rule or some crazy theoretical stuff I read somewhere that would get me even more mocked than I'm already looking forward to. Something about cantrips in the other thread threw me off I think...yeah, sure, that must have been it...
Expect posts about "OMG! Casters novaing nothing but their highest level spells! The Brokenness!"
Personally I think the novaing issue gets overblown. After all, for the first couple of levels all casters pretty much do is nova.
I'll admit I'm not much of a spell-caster which is why I can always use some serious input when I start brain-storming along these lines. In my experience, though, the players who only focused on their highest level spells would paint themselves into corners anyhow. I think the current HP vs. fatigue penalty also discourages some of that and they'll need to be thinking what they'll be able to eke out when they start pushing towards their threshold.
If anyone has any ideas on how to discourage nova-spam with a system like this, let's hear it.
There's also this little fact. Based on hp as originally proposed, those classes with d8 hit dice (bards, clerics, druids, etc.) have more effective casting stamina than those with d6 hit dice. If that makes a difference, that's up to you to decide. I also wondered about this scenario:
Cleric normally has 100 hp. He's been badly injured in a fight, he's down to 5 hp. He says, 'hey, I'm casting heal'. Does the fact he's throwing a 6th level spell (we'll assume he's been busy today) knock him over before he regains hp?
One other thing: figure out how many hp a given casting class has at a given level. Use average hp (3.5 for d6 hit dice, 4.5 for d8, etc.), modify for Con and favored class. Then figure out how many levels of spells at each of those given levels spellcasters have. Spontaneous casters can throw more spells per day, they'll have more than prepared casters. I imagine there will come a threshold fairly quickly where spontaneous casters can't empty out all their spells in a day w/o falling over, and the prepared casters will only go a little longer before the same. I mean, a 20th level cleric can throw 5 9th level spells each day, for 45 points of accumulated energy-stress. Then 40 for 8th level, 35, etc. And that's w/o bonus spells. There are guidelines for the number of encounters the average PC group should meet each day before needing to recover. Now, they'll start having stamina issues from another source besides the typical hp and spells resources, even if they don't nova.
There's also this little fact. Based on hp as originally proposed, those classes with d8 hit dice (bards, clerics, druids, etc.) have more effective casting stamina than those with d6 hit dice. If that makes a difference, that's up to you to decide. I also wondered about this scenario:
Cleric normally has 100 hp. He's been badly injured in a fight, he's down to 5 hp. He says, 'hey, I'm casting heal'. Does the fact he's throwing a 6th level spell (we'll assume he's been busy today) knock him over before he regains hp?
The different class Hit Dice poses a balance problem that's intrinsic to any HP-fueled spell system. I can't see a way to fix that aside from barring classes or tracking it with some value besides HP.
By using a separate Fatigue value that tapped out at max HP as opposed to current HP, I was specifically trying to avoid that healing scenario, since it gets even sillier when it's someone else healing the caster, especially with basic first aid. "Ranger, quick! Patch me up for another magic missle! I think I've space for another bandage there on my shin!"
One other thing: figure out how many hp a given casting class has at a given level. Use average hp (3.5 for d6 hit dice, 4.5 for d8, etc.), modify for Con and favored class. Then figure out how many levels of spells at each of those given levels spellcasters have. Spontaneous casters can throw more spells per day, they'll have more than prepared casters. I imagine there will come a threshold fairly quickly where spontaneous casters can't empty out all their spells in a day w/o falling over, and the prepared casters will only go a little longer before the same. I mean, a 20th level cleric can throw 5 9th level spells each day, for 45 points of accumulated energy-stress. Then 40 for 8th level, 35, etc. And that's w/o bonus spells. There are guidelines for the number of encounters the average PC group should meet each day before needing to recover. Now, they'll start having stamina issues from another source besides the typical hp and spells resources, even if they don't nova.
Actually, the energy-stress accumulation I'm proposing is equal to the level of the cast spell multiplied by 3. A 1st-level spell is worth 3 points of stress, a 9th-level spell is worth...*counts on fingers*...27 point of stress, so the cleric casting 5 9th-level spells would be accumulating...*counts on toes too*...135 points of stress. A 20th level cleric should be able to pull off maybe 3 9th level spells plus some change depending on what they put into CON. That's still pretty icky from an anti-nova standpoint, but sounds about right for what they should be capable of at 20th level while using any sort of spell point system.
This is also meant to be used as an alternative to the typical spell resources. I wanted something simple you could add too and compare to two other numbers every time you cast a spell. Because of the simplicity, that's the aspect that's more important to me than tying it to HP.
I also had an inkling of an idea to use some sort of wound check based on primary caster attribute like some games without HP do. You'd theoretically have no limit on number of spells per day, but every time you cast a spell, you have to make a control check or lose the spell and take a "wound." Certain wound levels have hard-wired penalties, if you tap yourself out, your brain is fizzled. That could just be a hard number for everyone with different classes offering bonuses to control checks, maybe.