I bet this isn’t very original, but it occured to me that spell levels is a good way of guaging, approximately, what an adventuring party is capable of in old-type D&D. Specifically, looking at the highest-level spells a magic-user will be able to cast tells you about the most impressive trick a party can single-handedly pull once. Thus an appropriately challenging adventure can be designed, for instance, by requiring that trick be pulled twice. Meanwhile in bigger adventure settings, like megadungeons, where the party is expected to extract and return multiple times, they can accomplish these several times over. The point is not to design adventures 1:1 around your party’s spell caster(s), but rather to treat the effects of one of their most powerful spells as an approximate measure of situation that will impose a significant resource drain. Note that I’m theorycrafting here and none of this is tested. I could be totally off here.
Still, let’s try it out. I’m an impatient person, so I’m going to use a few hand-picked spells from each level as examples rather than working through the whole list:
Sleep tells you a lot about the kind of combat challenges you can throw at this party. It can unfailingly take out 7 HD worth of enemies, give or taking, assuming none of those enemies have more than 3 HD. (Incidentally, a group of one 3 HD enemy and two 2 HD enemies feels like a nice challenging mix for a coordinated 1st-level party). You could increase the number of enemies to make for a really nasty fight that will require sophisticated planning and/or some very lucky rolls. Since Sleep affects targets in ascending order of HD, it can also act as a way of clearing out mooks led by stronger foes, allowing players to balance the odds in a scenario stacked against them.
Obviously turning an enemy into an ally is always a good moment, but from an adventure design perspective Charm person is most interesting for its limitations. First, the restriction to the category of persons excludes all the non-humanoid beasties, as well as undead. These must be dealt with by other means.
Second, charm takes a save that scales to the target’s HD. This means that lower-power targets are more likely to succumb to the spell. Note also that subjects are allowed subsequent saves at given intervals based on their intelligence. This means the ideal target for a charm person spell is a fairly stupid and weak target with high tactical value. Maybe a goblin in a machine gun nest in the middle of a skirmish, or a scout that knows how to navigate a labyrinth without getting lost or bumping into a Minotaur.
The wider implications here are a bit harder to guage than sleep, but this seems safe: a first-level party can probably accomplish any goal a low-level insider could without exposing themselves by dropping this spell. Give this party a challenge that rewards having a friend on the inside, but pay attention to what such an insider can’t do.
Of course, a party could conceivably nail any “person”-type target, but the odds are worse the more HD they have. Charming the local leader is higher risk, but higher reward, and not subject to the same HD limitations as sleep. Give some thought as to what happens if the party wins over the person in charge and the general chain of command. And what happens if the underlings know their leader is charmed? Here’s another reason it can be important to have multiple factions – and perhaps even an unruly subfaction waiting for an excuse to splinter.
It’s worth noting that a 1st-level M-U with an extremely basic utility spell has favourable odds to temporarily blind any sighted target with less than 10 HD. Consider throwing some real nasties their way – just make sure they have the option to run.
Ok I was going to cover level 2 in this post too but it turns out the implications of Phantasmal Force require a PhD in imaginary philosophy to parse and I ran out of steam. I’ll return to this soon maybe send post