A System of Magic
A bolt-on magic system for tabletop role-playing games
Last night, I started fiddling around with an alternate magic system for tabletop RPGs. This can be dropped into any game as a magic system.
(I recognize this is a bad idea for some RPGs and some groups.)
I wanted a spell system in which a spellcaster imagines a spell effect (which may be limited to a domain or a set of effects), maybe takes some time to prep, then casts the spell, and something pretty close to the intended effect occurs, most of the time. It may not last as long as desired, or it may be much more powerful, or it may effect fewer pepole than anticipated.
This implies a system in which spells can be affected along several dimensions. So, let’s define six and a half dimensions: Preparation Time, Distance, Duration, Damage, Number of Targets, Number of Effects, and Visible Manifestation (the half, which has no mechanical impact). Each of these has a point cost “ladder.” For example, targeting only one person costs 0 points, but every additional target adds 1 point of cost.
A “default” spell—one that has a mild effect on only one person, takes a little time to prepare, and lasts briefly—has a total cost of 0. You can push any of those dimensions up or down to change the cost.
This point cost is the spell’s intended difficulty.
Then we get into the math. I love the Fate dice distribution, and I wanted something similar, so I played around with that. What I came up with looked like heavy math until I actually did it, and I found it was easy.
Roll 2d6. Then roll 2d6 again and subtract it from the first result. Then subtract the spell’s intended difficulty.
Note: your spell’s intended difficulty might be negative, which will effectively increase the result. That’s good. You want that.
The result of the roll is the spell’s actual difficulty. If it’s less than the intended difficulty, the player has to decreases some dimension(s) of the spell to get it within the difficulty. If it’s higher, the player gets to pump the spell up.
Now, here’s where I geek out about the numbers. 2d6-2d6 is actually pretty easy to calculate in your head, because 2d6 tends to roll around 7. So usually, you’re just calculating 9 minus 7 or 6 minus 8. That’s grade school stuff.
Le’ts talk about that difficulty. If you have an intended difficulty around 0, you’ll usually get a result near 0. But if you have a difficulty way higher than 0, you’ll tend to get even lower results than your difficulty. So big spells are even harder.
You don’t want to build your spell from scratch every time, so the game would include a handful of classic spells.
Of course, there’s plenty more to write about here: actual point cost on each dimension, spell limits (how many spells can you cast a day?), leveling up, modeling odd spell effects like summoning or teleportation, and so forth. But them’s the basics.
(Photo credit: http://www.flickr.com/photos/52798669@N00/3248483447/ — CC-BY-2.0)
