Mana Cost for Homebrew System

[Maat Mons]

I’ve been considering a system where spellcasters all have the same size mana pool, but more powerful mages get mana cost reduction.

This is inspired by World of Darkness games. If you’re not familiar with that system, everyone has six Hit Points, but everyone also has a Stamina score. Whenever you take damage you roll a number of dice equal to your Stamina score, and each success rolled subtracts from the damage you take, to a minimum of zero. Or something like that. It’s been a long time since I played.

What I’m trying to figure out is, should you be able to try to cast a spell if a bad roll would mean you’d need to pay more mana than you have left? What would happen if it turned out you couldn’t pay the cost? Would the spell just fail? Would you temporarily burn out your magic? Would you suffer some long-term drawback?

I’m leaning towards not letting someone even try to cast a spell unless they have enough mana to cover the maximum possible cost they’d incur from the worst possible roll. This would mean that, as a spellcaster becomes more worn out, they lose access to their more powerful effects. Even if you have a chance of reducing a six-mana spell to zero mana cost, you’re still hard-locked out of casting it when you only have one mana left. What behaviors would this encourage? If mana replenishes once per day? If mana can be replenished multiple times a day?

With this mana system in place, would it be advisable to also have a stamina system that parallels it for fancy weapon maneuvers? If the physical side of things has both stamina and hit points, should the mental side have some second pool too? Sanity maybe?

If the game has four ability scores, Strength, Finesse, Wits, and Magic, with Strength governing hit points, and Magic governing mana points, would there be any logical pools of resources for Finesse and Wits to govern? I’d almost rather have Finesse govern fancy weapon moves than Strength, but then the pool of resources really shouldn’t be called Stamina.

[MrStabby]

I think I would be tempted to allow casting if spells you don't have the mana for, but you make up the deficit with life (at some exchange rate). You are really playing with fire if you do this, and it's a desperate measure.

[nonsi]

I’ve been considering a system where spellcasters all have the same size mana pool, but more powerful mages get mana cost reduction.

The problem with this approach is that there aren't small numbers that divide well enough for you to find an elegant and simple to use solution.
I tried several solutions myself to see if this approach can work and never found one that did (I'd be happy to be proven wrong)

The simplest solution I've found for Mana pools and the only one that actually seems balanced power-wise to me, is the "Spell-Points" approach suggested here:
https://forums.giantitp.com/showsinglepost.php?p=18777377&postcount=4

If you wish to explore spellcasting against difficult conditions, you can draw inspiration from the "Strain & Tolerance" (same post).
This is actually closer to what you're looking for in terms of better casters having to pay less, but notice that the pool size is not fixed, but rather still relies on level and stats.
Of course expanding your game options comes at the expense of simplicity. If you find the "Strain & Tolerance" system not too much to process (I think most should be able to cope with it), it could be a decent solution for you.

[Maat Mons]

I’m hesitant to allow people to spend HP to fuel magic, because I plan for magic to be able to heal HP. If anyone ever gets to the point where they can pay less HP to cast a healing spell than the spell heals, they'll kind of stop having any limit on how much they can use magic.



Looking at the Strain and Tolerance system, I see the following:

Spells have a base Strain cost of Spell Level * 4/3 + 5 (rounded up)
Full casters reduce strain costs by Class Level / 2 (magnitude of reduction is rounded down, or equivalently, total strain paid is rounded up)
Partial Casters reduce Strain cost by Class Level / 3 (rounding is inconsistent)
Witches pay increased Strain cost for some Secondary Circle Spells (equivalent to treating the spells as higher level)
Full Casters reduce Strain cost of Cantrips/Orisons by 1


If the rounding inconsistencies were fixed, the tables could be dispensed with.

[nonsi]

I’m hesitant to allow people to spend HP to fuel magic, because I plan for magic to be able to heal HP. If anyone ever gets to the point where they can pay less HP to cast a healing spell than the spell heals, they'll kind of stop having any limit on how much they can use magic.


On one hand, you could deal with this problem by stating that HP used for powering spells are not injuries, therefore they only heal naturally when you're otherwise fully healed.
But you'd have to make sure that paying for mana with HP is really taxing and that players would only draw that card in cases of dire straights.





Looking at the Strain and Tolerance system, I see the following:

Spells have a base Strain cost of Spell Level * 4/3 + 5 (rounded up)
Full casters reduce strain costs by Class Level / 2 (magnitude of reduction is rounded down, or equivalently, total strain paid is rounded up)
Partial Casters reduce Strain cost by Class Level / 3 (rounding is inconsistent)
Witches pay increased Strain cost for some Secondary Circle Spells (equivalent to treating the spells as higher level)
Full Casters reduce Strain cost of Cantrips/Orisons by 1


If the rounding inconsistencies were fixed, the tables could be dispensed with.


Notice that the higher spell level groups have higher starting costs.
That's intentional, because gaining access to higher level spells comes with a significant power boost.
I don't see a workaround for that.

While the Strain & Tolerance solution is the best narrative-wise (for telling the story of Raistlin Majere for instance) for my personal taste the proposed Spell-Points solution is the best cocktail game-wise in terms of simplicity, versatility, elegance and balance.
For me, it's the best "value for dollar" solution. It gives the players a lot of options mid-game, it limits going NOVA frequently (because this will render players to be shooting blanks afterwards) and it requires the least amount of bookkeeping. The only downside is that you can't overtax in cases of "do-or-die".

[Maat Mons]

Now that I think about it, I'm trying to design a system where, in principle, all mana costs can go to zero with enough investment anyway. So maybe it's not a problem if there exists another way to get unlimited casting. Still, I kind of like keeping HP and MP separate. But I'll think about it.

The idea of mana-overdraw-based HP loss being different from other HP loss reminds me of another point. I was planning to have people roll "toughness," or whatever, whenever they take damage to potentially reduce the damage. If people get to roll to reduce the mana cost of the spell, and then roll again after converting that mana cost into an HP cost to reduce the damage taken, They're kind of doubling-up on reductions. I'm not sure I want that.

I'm leaning towards having the spell fizzle if you don't have enough mana. But I'm not sure if I should punish the failure by having all remaining mana be expended, or having casting burn out temporarily, or just let people keep trying over and over again until they get a good enough roll to reduce the cost to something they can pay. Maybe ding one mana for each fizzle, and if you don't have one mana to ding, temporary burnout?



I don't see any problem in having the "starting cost" of spells increase. Basically, you just have the base cost of higher-level spells outpace the cost reduction given by the class. Here, I made a table.





Total Cost (Base - Reduction)


Level
Cost Reduction (Lvl / 2)
0
(base cost 5)
1
(base cost 7)
2
(base cost 8)
3
(base cost 9)
4
(base cost 11)
5
(base cost 12)
6
(base cost 13)
7
(base cost 15)
8
(base cost 16)
9
(base cost 17)


1
0
5
7
-
-
-
-
-
-
-
-


2
1
4
6
-
-
-
-
-
-
-
-


3
1
4
6
7
-
-
-
-
-
-
-


4
2
3
5
6
-
-
-
-
-
-
-


5
2
3
5
6
7
-
-
-
-
-
-


6
3
2
4
5
6
-
-
-
-
-
-


7
3
2
4
5
6
8
-
-
-
-
-


8
4
1
3
4
5
7
-
-
-
-
-


9
4
1
3
4
5
7
8
-
-
-
-


10
5
0
2
3
4
6
7
-
-
-
-


11
5
0
2
3
4
6
7
8
-
-
-


12
6
0
1
2
3
5
6
7
-
-
-


13
6
0
1
2
3
5
6
7
9
-
-


14
7
0
0
1
2
4
5
6
8
-
-


15
7
0
0
1
2
4
5
6
8
9
-


16
8
0
0
0
1
3
4
5
7
8
-


17
8
0
0
0
1
3
4
5
7
8
9


18
9
0
0
0
0
2
3
4
6
7
8


19
9
0
0
0
0
2
3
4
6
7
8


20
10
0
0
0
0
1
2
3
5
6
7



Other than the cantrip column, that exactly matches the table you made for full casters. I generated every cell for total cost by taking the base cost for the spell level, from row 2, and subtracting the cost reduction from class level, from column 2. For example, 9th-level spells cost 17 mana as the base, and at level 17, when you can first access 9th-level spells, you subtract 8 from the costs of all spells, so your "starting cost" for 9th-level spells is 9 mana.

Tangentially, does anyone know how to make a cell span multiple rows? I can only figure out how to make a cell span multiple columns.

[Just to Browse]

The critical distinction between overdraw fizzling vs overdraw succeeding at a cost depends on the sorts of long-term play patterns you want to see. If there's a random chance to overdraw and overdrawing on a spell causes a fizzle, overdrawn spells mean lost action economy. If your game is anything close to a modern fantasy TTRPG, action economy is a massive cost, which will encourage players to be more conservative with their mana the closer they get to overdrawing.

If overdrawing a spell applies some alternative cost (such as HP loss, or a status condition), the cost becomes your balancing lever that determines whether and how often players will want to overdraw. A high cost leads to similar behavior as the "overdraw = fizzle" example. But if the cost is minimal, players are encouraged to begin their adventuring day judicious and then drop a big super move at the end of the day. The specifics of the cost create a spectrum of behaviors here; if you had no cost at all, players would usually end their day with the strongest spell in their arsenal. Is that something you want to encourage? I think it's worth considering.

It's probably worth noting player skill here. HP and most debuffs tend to be overvalued by lower-skilled players across all games because it feels important, and action economy tends to be under-valued, so the patterns I've described above will probably be flipped for less enfranchised players.

[nonsi]

Tangentially, does anyone know how to make a cell span multiple rows?


IIRC, you can put a table inside a cell and do with it whatever you want.
You can even put in into a spoiler block if you want the option to collapse.

[Melayl]

Here was my take on a mana-based system, for whatever it's worth to you. It's an old thread, so the tables are broken.

https://forums.giantitp.com/showthread.php?140759-Melayl-s-mana-based-spellcasting-system-3-5-PEACH

I have a skill-based casting in my sig, but those tables are broken, too.

[Deepbluediver]

The problem with this approach is that there aren't small numbers that divide well enough for you to find an elegant and simple to use solution.
I tried several solutions myself to see if this approach can work and never found one that did (I'd be happy to be proven wrong)
I agree with this ^

Mana-cost reductions work well in computer-games where mana pools can run into the hundreds or thousands and all the calculations are handled automatically, but for table-top pen-and-paper games I've never seen one that worked decently without requiring players to keep a pocket-calculator on hand. That's not a BIG ask, but in a combat where players are rolling lots of dice, if you haven't done the math ahead of time it can be a real pace-killer. Even stopping to consult a chart can be a turnoff if it's just one type of player doing it all the time.

Practically speaking, increasing the size of a player's mana-pool and decreasing the cost of their abilities have the same effect. Yes they can be fluffed a little different and in some games the different mechanics have niches uses. For example anything that targets X% of your mana pool or depends on how much mana you spend to cast something will play out differently, but both of those types of mechanics are ALSO relatively rare (in my experience) in D&D style games, so here the difference is minor.

If you can make it work I'd be curious to see the final product though, if only to loot it for ideas.

[Maat Mons]

I wasn’t figuring on it being a %-based reduction. More like “I roll 6 dice for mana cost mitigation, 2 successes, that means I subtract 2 from the mana cost.”

If you did want things to be %-based, at least on average, you could roll a number of dice equal to the spell’s base cost, trying to roll under your Magical Endurance stat, and lose a point of mana for each failure. Though that would only feel at home where more dice = more bad was normal, and everything was degree of failure, not degree of success. “The enemy hits you with a 7-base-damage weapon, so roll 7 dice, trying to get under your Toughness, and take a point of damage for each failure.” Feels really backwards.

It occurs to me that a mana point saved is a mana point earned. That is, decreasing per-round mana expenditure by 1 is a lot like regenerating 1 mana each round. I could have every spell always cost the full amount of mana, and then have the player roll once per round to see how much mana they regenerate. If the player is casting one spell per round, that works out similarly to my idea of rolling to decrease mana cost for each spell. I mean, it makes out-of-combat casting free, but that was kind of already the case with someone at 0 MP trying over and over to cast a spell until they finally roll well enough to completely negate the cost. Not sure that I want everyone always starting every fight at full power though.

I suppose I could try something more peculiar, where every spell, no matter the level, has a cost of 1 mana point. The only scaling would be in the odds of negating that cost. So, with a high-level spell and/or low skill, you’d almost certainly lose the mana point. But with a low-level spell and/or a high skill, you almost certainly be able to cast it for free. At least this way, I could say you must have at least 1 mana remaining to attempt to cast a spell, and I’d never have to worry about someone having insufficient mana to pay for the cost on a bad roll.

[Morgaln]

If players can reduce mana costs to 0 through their roll, then you are not introducing a cost system, you are introducing success rolls for magic. Mana is a bonus resource that you can use to buy extra successes in case your roll wasn't good enough, but it is not a cost you need for spell casting under that kind of system.

This might be entirely what you intend/want, I just felt I should point that out.

[JeenLeen]

As basically already noted, but I want to emphasize something: if you allow overdraw with a cost, you need to avoid two issues.

1) the penalty being so minor it basically doesn't matter. (Or players can loophole it away.)
You address this with the healing-spell-cost thing discussed.

2) the penalty being so dire players dare not risk it
I see this mostly in permanent corruption in some systems, or like how Warhammer has the potential for psykers to just die when casting a spell.
I think losing action economy... well, I remember playing oWoD: Mage and it really, really stunk when I failed my roll to cast a spell and lost action economy. It's not a terrible tradeoff, but annoying and disappointing.

You seem to be balancing these pretty well.
If you go "magical harm has to heal naturally and can't be healed by magic", take downtime into consideration for the theme of the game. WoD (at least how I played, which was mostly Mage with Paradox damage at times) assumed downtime between missions that allowed healing time. Healing shouldn't be a given -- stuff can be urgent or come up -- but if you might overdraw 10% of the time, you should have downtime about 10% of the time.

[Deepbluediver]

I wasn’t figuring on it being a %-based reduction. More like “I roll 6 dice for mana cost mitigation, 2 successes, that means I subtract 2 from the mana cost.”

If you did want things to be %-based, at least on average, you could roll a number of dice equal to the spell’s base cost, trying to roll under your Magical Endurance stat, and lose a point of mana for each failure. Though that would only feel at home where more dice = more bad was normal, and everything was degree of failure, not degree of success. “The enemy hits you with a 7-base-damage weapon, so roll 7 dice, trying to get under your Toughness, and take a point of damage for each failure.” Feels really backwards.

It occurs to me that a mana point saved is a mana point earned. That is, decreasing per-round mana expenditure by 1 is a lot like regenerating 1 mana each round. I could have every spell always cost the full amount of mana, and then have the player roll once per round to see how much mana they regenerate. If the player is casting one spell per round, that works out similarly to my idea of rolling to decrease mana cost for each spell. I mean, it makes out-of-combat casting free, but that was kind of already the case with someone at 0 MP trying over and over to cast a spell until they finally roll well enough to completely negate the cost. Not sure that I want everyone always starting every fight at full power though.
That's interesting- it seems workable in the absolute sense but I feel like it's introducing a lot of extra dice-rolls and math for relatively little gain. And if some classes are rolling a lot more dice and taking longer to figure out their turn than others, I'm not sure it's good overall. It also definitely attracts a certain type of player, and repels others, which kinda feels like a soft-lock on accessibility.

I was GOING to say something like "why not just roll 1 dice, like a d4 or d6-1 and subtract that cost from the spell? and then make the dice bigger or more numerous as appropriate". But your mana-regen idea is basically just that in reverse; its the same thing with different fluff. And again, it CAN work, I'm just not convinced that the added rolling and adding/subtracting is worth the benefit, compared to the thing I mentioned in my original post- simply making your mana pool bigger.


I suppose I could try something more peculiar, where every spell, no matter the level, has a cost of 1 mana point. The only scaling would be in the odds of negating that cost. So, with a high-level spell and/or low skill, you’d almost certainly lose the mana point. But with a low-level spell and/or a high skill, you almost certainly be able to cast it for free. At least this way, I could say you must have at least 1 mana remaining to attempt to cast a spell, and I’d never have to worry about someone having insufficient mana to pay for the cost on a bad roll.
What Morgaln said- IMO that's a very succinct way to think about it. If it helps, imagine how this system would play out if applied to a martial class for comparison. Suppose you took something like Barbarians RAGE! or a (5E) Fighter's Second-wind feature and gave them a chance to recover a spent use immediately upon using it. If it sounds awful or feels like it would break the game, then maybe step back and consider why the same mechanic applied to two different class-models comes across so radically different. And if you can't satisfy yourself, then what will your player's think?

There's lots of stuff you CAN do to make the game different, and I support it up to a point. I'm happy to play in a game where you've got lots of different systems with moderate variations on the same theme. To use D&D 3.5 as an example there's Vacian casting, Invocation, Powers (psionics), Maneuvers, Shadowmagic, ....deep sigh....Utterances, .... and probably something else I've missed, etc etc etc, that all basically replicate bog-standard spellcasting, with emphasis on different aspects.

It's just in this one particular space, trying to apply cost-reductions to ability-usage seems like it might be over-reaching. That there's no really good way to do it that hits the trifecta of "fun, balanced, and simple".

[Theodoxus]

It's just in this one particular space, trying to apply cost-reductions to ability-usage seems like it might be over-reaching. That there's no really good way to do it that hits the trifecta of "fun, balanced, and simple".

But does it really over-reach? I remember when 5E came out, a lot of people lost their spadoinkle over the idea of cantrips actually doing decent damage that scaled. Coming over from 3.PF, I thought it was pretty awesome, personally.

While I do agree it tends to be difficult emulating a CPRG's mana style system of slow regeneration over time, there really isn't a reason why nigh unlimited use abilities can't exist in a game, even spell casting (see cantrips above).

Don't want everyone spamming Fireball? Build in limits. Take a page from PF2; their Barbarians can rage all day long, as long as you take a 10 minute break between uses. Cast Fireball? (or any leveled spell), can't cast that spell again for some period of time. Make it 1 minute, and they become encounter powers. Make it 10 minutes and they become every other encounter in a dungeon, and encounter in a more spread out environment.

Still too powerful? Make it 'Vancian-lite', where you have to prepare the number of uses of a specific spell per iteration. Not the slots themselves, those remain flexible, but if you want to cast two fireballs in a single time frame, you need to 'store' two fireballs in your prepared spell allocation. Some players will play a caster as a swiss army knife, having 1 prepared casting of most of their spells, in preparation for 'anything that might arise' while others will maximize the number of 'best spells' at a cost of flexibility.

Of course, this would all be better built from the ground up rather than trying to shoe-horn it into an existing paradigm, but if the same basic idea carried over to the martial classes, I think it might work. Things like sneak attack might need to be boosted to be allowable on any qualifying attack, not just once per turn; rage, as noted, would be usable with a small downtime requirement. Ki powers might no longer require Ki, though Stunning Strike might need a small nerf if that were the case - usable on a single target per round, at a minimum.

It's definitely doable. Just requires a shift in thinking. And a definite understanding of exactly what you're trying to accomplish.

[Amechra]

I remember when 5E came out, a lot of people lost their spadoinkle over the idea of cantrips actually doing decent damage that scaled.

To be fair, they lost their spadoinkle because people tend to overvalue dice and undervalue flat bonuses when it comes to damage.

...

Something you could do to get the "slow mana regen" feel without needing to actually have a mana pool is borrowing soaks from Urban Jungle (which does something similar for HP).

In that game, any attack that deals any damage to you takes you out of a fight. However, characters get a number of abilities called "soaks" that can each "soak up" a specific amount of damage, which each have different recovery conditions. Those conditions can vary from "just take the Recovery action" to "hit an enemy with an attack" to "sleep it off".

This seems pretty simple to transfer over to your "spells have a cost and you get a roll to reduce it" thing — instead of having a mana pool, paying any amount of cost temporarily burns out your magic. However, every spellcaster gets some number of "Arcane soaks" that they can expend to eat up costs (on top of the roll). Then you'd just give them some thematic recovery conditions:

Arcane Fatigue (-2): Recovers when you take a rest.
Implement Failure (-2): Your staff (or whatever) explodes. Recovers when you find a new magic staff.
Minor Warlock Soak (-1): Recovers when you do a minor favor for your patron.
Major Warlock Soak (-3): Recovers when you do a major favor for your patron.
Wild Surge (-4): When you use this soak, roll on the wild magic table as your magic goes wild. Recovers when you take a rest.

If you wanted to, you could go even further and make it so you need to have more successes than the cost for the spell to go off, with successes+soaks = cost resulting in just a failure (vs. failing and burning out if successes+soaks < cost).