While the Rats & Ratlings booklet of our D.I.Y. D&D has pretty much all of the rules we’re using, including the rules for clerics and magi casting spells (and they are the only spellcasting classes), the spells are broken out into two separate booklets…Gods & Gophers and Mice & Magic. The goal was to keep spells and casting pretty simple. I also leaned pretty heavily on Dungeon World, especially for success, failure, and success with complications.
My old gaming group “back in the day” rarely played D&D with the standard spellcasting rules. We implemented a little system where a spellcaster had a percent score that increased as the spellcaster increased in level. To cast a spell, you rolled a d100 and if the result was less than the percent score, the spell was successfully cast AND the score went down by a certain amount (more for higher level spells). Rest brought the score back up. So it was a system where a caster could cast a lot more spells but there was no guarantee that the spell would always be successfully cast. It worked for us back then.
Now, however, I went with an approach that fit into a more d20 mechanic. Clerics and magi both prepare spells each day (clerics can select from their full spell list while magi pick from those spells in their spellbook). To cast a spell, a d20 is rolled plus WIS or INT (as appropriate) plus level minus the level of the spell being cast (spells are 1st, 3rd, 5th, etc. level). On a result of 15 or higher, the spell is cast successfully. On a result of 8 or less, the casting fails. On a result of 9 to 14, the spell is cast but there are complications. The player has to choose from one of three complications (a la Dungeon World): lose the spell, take a -2 penalty to all spellcasting checks going forward (until the caster prepares spells again), or, with my permission, draw unwelcome attention to them. That last one has taken our game in directions that I was not thinking about a few times already. The choice of three has also been agonized over quite a bit which has been absolutely fantastic…I think meaningful game choices like this are good things.
I’ve also applied the concept of “tags” to spells and tried to streamline their descriptions. A simple spell like Detect Magic just reads, “Persons, places or things with an enchantment are briefly outlined in an aura that you can see,” and has the tags Instant, Near, and Personal. This means the spell’s effect occurs instantaneously, things up to 30 feet away that are magical have the aura, and only the casting mage can see them. Fireball has the tags: Burst (Medium), Far, Instant, Resisted and has the description, “A ball of fire explodes outward with a low roar, centered on the location you selected. The fire does 3d6+10 damage to every creature in the area. If a creature succeeds at a DEX check, the damage is halved.” Far means the spell can target a location up to 200 feet away. Burst (Medium) means the spell’s effect fills a 20-foot radius area. Resisted indicates that the spell can be resisted or partially resisted with a successful check by a targeted creature (in this case, half damage with a successful DEX check).
That’s pretty much it. The spell lists are pretty iconic (to me at least) and are a bit pared down. Ranges fall into three categories: Touch, Near, and Far. There are no durations to track. Spells pretty much either Instant or Ongoing with the latter applying a -2 penalty to spellcasting checks while the spell is ongoing (penalty is cumulative). Tracking and bookkeeping for spells are pretty minimal.
This approach has worked pretty well for us so far.
