Limiting a Magic System
Continuing thoughts on a drop-in magic system for tabletop RPGs
With the system of magic I introduced in my last article, spellcasters can cast spells as often as they like, as long as they wait for the appropriate preparation time. This may be exactly what you want, so let’s not introduce any further limitations to the basic system.
But what if you want magic to be more limited? What if you want to model exhaustion?
A simple mechanic for exhaustion is a mana pool. Each spellcaster has a certain number of points for spellcasting, and when the points run out, the caster can’t cast spells. The mana pool refreshes at some rate.
How many points? Let’s subtract the spell’s difficulty from the mana pool. Every day, a spellcaster re-gains some percentage of their mana pool.
There are some very interesting things you can do with this by changing the mana pool size and refresh rate, but first, let’s address an issue caused by this particular system. Spells can have a negative cost, remember, which technically would recharge the mana pool when cast!
This actually would be an interesting effect. Spend a lot of time preparing a very simple spell, and your effort is rewarded with a little extra mana for your next spell. Assuming, you don’t want that, though, simply give each spell a minimum cost, say, 1 point of mana.
Now, on to those refresh rates. We can fiddle with a lot of dials here: initial mana pool size, refresh amount, refresh frequency, and increasing the mana pool size when you “leveling up.” Refresh rate and size are linked—you can refresh seven points a week or one per day—and while that’s an interesting difference, let’s not dive into those minutae just yet.
So let’s look at a couple different manifestations:
Large pool, fast refresh. Spellcasters can attempt very difficult spells, and they will only exhaust themselves after large amounts of truly Herculean spells. Note that the dice mechanic still makes powerful spells hard to pull off, so even if a caster attempts a 15-point spell, he or she will rarely be able to pull it off. So they won’t hit the limit quickly.
Large pool, slow refresh. Spellcasters can attempt very difficult spells, but once they’re exhausted, they can only attempt small effects for a while. This is arguably more “realistic,” since it gives spellcasters plenty of options, without allowing daily chats with Elder Gods.
Small pool, fast refresh. No spellcaster can pull off huge spells…but they can all attempt reasonably-sized spells all the time. Combine this with a logarithmically larger mana pool as the character levels up, and you perfectly model the seduction of magic: minimal effects early on, with the promise of great power in the future.
Small pool, slow refresh. You can’t do much, and when you’re done, you’re done. This is more like the gritty fantasy of Conan.
As a default, let’s give spellcasters 20 points of mana, which refreshes 5 per day, and a minimum spell cost of 1 mana per spell. That lets them pull off quite a few spells every day, but if they fire off several large ones, they’ll need a few days to recharge.
I also mentioned leveling up, but let’s leave that for the next article.
