Spell casting systems and resource management

 A character's spells are an important resource, both for the individual and the party. As such, a big part of the game's challenge comes from managing them well, and different schemes offer different incentives in play. Below, I compare and contrast the differences between some common spell casting systems, with special attention to their effects on resource management and player decision-making.

Prepare and forget: The by-the-book method for most older editions of D&D and their modern clones and simulacra. Choose spells for your caster to prepare or memorize each day. Those are the spells you get, and when you cast one, it disappears from the caster's mind until prepared again after a full rest. You can choose to prepare multiple instances of the same spell, if you want to be able to cast it more than once. 

In theory, this is Hard Mode resource management: your spells are limited and you have to choose them in advance, with imperfect to nearly nonexistent foreknowledge of what will and will not be useful. In practice, players will almost always choose the same generic slate of broadly useful spells while shunning niche spells which might be situationally very potent but are less likely to see use in any given adventure. This is not a failure of player creativity, but a natural consequence of basic, rational risk/reward analysis. The magic-user loaded up with magic missile and sleep spells will almost certainly get a chance to cast them, and they will almost certainly be helpful, while the one who chooses read languages and floating disc may be relegated to lobbing the occasional dagger while waiting for an opportunity to shine that might never come. The cleric who fills her spell allotment with cure light wounds is nearly guaranteed to be called upon to cast them, and in fact the rest of the party will expect her to do so, to the point it would be downright foolish to waste even a single slot on detect evil or purify food and water. As trite and boring as it is to be the party healbot or sleep-monkey, it's even worse to play a spell caster who doesn't have meaningful opportunities to affect the outcome of an adventure at all because he chose the "wrong" spells.

If you want to nudge characters into very familiar and fairly rigid roles, casting the same two or three spells from each spell level over and over again, this is the mule to get you there.

At-will casting: So far as I know, this doesn't appear in any old edition of D&D, but rather is a development of newer editions, usually applied to zero-level spells or cantrips. In older editions in which cantrips exist at all, they're not only at least somewhat limited, they barely qualify as resources, being primarily a bit of flavor, enabling casters to perform mundane tasks with a bit of magical flair. With "cantrips" providing potent game-mechanical effects, they definitely become a resource, but the management element is almost completely eviscerated. (Some vestiges of it may be retained if casters are at least required to choose which cantrip to "memorize" for the day, rather than casting carte blanche from among any and all they know.) Sometimes this is done as part of a scheme to bring casters onto the same playing field as fighters, whose attacks are a similarly unlimited resource. If you want the experience of playing different classes to feel much more similar, well, here you go. For those who prefer, even relish, the variety of play styles encouraged by different class mechanics, definitely look elsewhere. 

Spell points: Cast whatever you want, as many times as you want, as long as you know the spell and you have enough points for it. Typically, spell point cost goes up with the level of the spell; one point per spell level is common and intuitive. Rather than being selected in advance based on sketchy prognostication or generic probabilities, spells may be chosen in situ, in real time, with full knowledge of the situation of the moment. Niche spells are much more likely to be used in play, because you can just whip them out when you know for a fact they're relevant, instead of having to foresee situations and gamble that they will indeed come to pass and the spell won't simply be preempting a more broadly useful one. 

There is still a resource management aspect, with the actual resource being managed not being spells, but the amorphous pool of fungible spell points. One consequence of this is that those broadly useful spells, your sleep and cure light wounds, even fireballs for higher-level characters, can be spammed with relative impunity. At least with prepare-and-forget, the player had to choose those spells, with full knowledge that he was giving up utility spells that might have been useful. There isn't even the burden of choosing between extra iterations of sleep or a few more magic missiles. With spell points, there are no regrets!  This can really get out of hand if using the standard spell descriptions with effects scaling by caster level: a 1st-level spell like magic missile in the hands of a 9th-level caster can dish out 5d6+6 damage at the cost of a single spell point. Solving this problem can be as simple as doing away with level-based scaling or charging extra spell points to get the level-scaling benefits. 

Spell points do allow a lot more versatility, without completely unleashing casters from resource constraints, but it's a double-edged sword. It enables in-the-moment choices to cast niche spells, but it also enables "full auto" use of staple spells without even the implied opportunity cost of the prepare-and-forget method. This can be mitigated partly or entirely with adventures that feature a rich variety of challenge types, but if your game leans even a little disproportionately toward a particular sort of challenge (e.g. combat, puzzle, role-playing) it's going to encourage overreliance on particular spells.

Open slots: Similar to spell points in that it allows carte blanche casting from all the spells in a character's repertoire, but instead of a pool of completely fungible spell points, it utilizes the spell slots as listed in the RAW casting tables. If you want to cast cure light wounds, it takes a 1st-level spell slot. If you want to cast silence 15' radius, it'll cost you a 2nd-level slot, and so on. This system features a lot of the same strengths and drawbacks as spell points, but it's less mathy; rather than the act of casting a spell being a subtraction problem, it's simply crossing off a slot. Its chunkier nature also curbs some of the potential excesses of a spell point system: casting a low-level spell with a higher-level slot may or may not be allowed, but it typically doesn't grant any special benefits, and "cashing in" multiple low-level slots to power a higher-level spell is almost certainly not permitted. 

If the in-the-moment fluidity of spell points appeals to you, but you have reservations about just how loosey-goosey it is, this might be the casting system for you.

Cast till you fail: Spell casting requires a proficiency check, and as long as the checks are successful, the character can continue using that spell. If a check is failed, the spell is lost for a while, typically until after a full rest. The primary effect is to make resource management radically uncertain -- you never know how many times you'll be able to use a given spell. It could be dozens, or it could be zero.  

This system features prominently in Shadowdark RPG. It works fairly well with spells written specifically for it, useful but relatively limited. Powerful spells such as sleep or fireball, as traditionally written, would quickly become wildly unbalancing if a character has a high casting bonus or just hits a hot streak on the casting dice. 

The major down side, as mentioned above, is that there's a very real chance your spells will fizzle and you'll get nothing. (Then again, a 1st-level MU in traditional D&D could effectively get the same if the hobgoblin makes its save against his single charm person spell, so there's that. Still, in that system, a player could choose from a variety of spells that don't have a chance of failure, which isn't possible here.) In theory, the chance of losing the spell for the rest of the in-game day would encourage judicious casting, but my experience so far is that it encourages behavior not unlike a spell point system.

One interesting quirk of the system is that failure only nullifies the specific spell attempted; all other spells known are still in play until you fail rolls for them too. This means that having a larger repertoire of spells is a particularly helpful boon, and also that repertoires must be much more carefully managed by the referee if things aren't to spiral out of control. The more different spells a character has to fall back on when one is lost, the stronger the incentive to treat spell casting as a potentially limitless spell point pool.

Even so, with a list of well-balanced spells, robust rules for limiting spell repertoires, and players willing to embrace a high level of uncertainty, it can be a fun way to play.

Once each per day: Utilizes either a spell slot or spell point framework, but no single spell can be cast more than once per day. Why exactly this is so within the fiction isn't important, per se, at least no more so than why a caster "forgets" a memorized spell (or just a single iteration of a spell!) upon casting it. The important points are its implications for resource management and player agency.

This, in my opinion, is Hard Mode done right. It features both the versatility and freedom of spell choice in the moment, and robust resource management elements that force players to make interesting choices. Choosing before an adventure even begins in earnest whether to risk giving up a magic missile in exchange for a read languages is not particularly fun; it's either dull or stressful, depending on how tempted a player is by those niche spells. Choosing whether this moment, right now, is the best time to use read languages or charm person or magic missile is a lot more interesting. Unlike prepare-and-forget, the fact that a particular spell would be useful is immediately evident, but unlike other free-form systems, you have to decide if you want to use it now or later; you can't do both.  

The wonderful thing is that either way, there will be consequences, and the player may or may not have regrets, but regardless of all that, the player's choice to use that spell when he did had an impact on play. It wasn't wasted, as preparing a spell might have been under prepare-and-forget, and it wasn't so obvious a choice as to require no consideration, as might have been with pure free-form casting. It maximizes player agency, both in terms of making an informed choice and in terms of having real consequences in the game. As an added bonus, it incentivizes creative thinking, both in terms of conserving vital spells ("How can we get past this two-headed guard dog without using the sleep spell we might need later?") and making miscellaneous spells count when you've already burned the obvious ones ("There's a bottomless chasm in front of us, a band of angry lizard men behind us, what can I do with mirror image and spider climb?") All of this is why I'm planning to use this system in the next game I run, and I'll of course post my thoughts on any interesting and/or unforeseen results, for good or ill, after seeing how it performs in actual play. 

 




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