It may or may not be evident from playing in the campaigns I run here, but I have a fondness for picking over the 3.X Core Rulebooks in search of stuff that's incomplete, vague, or just interesting. And my love of random encounter tables is, uh, well-established. These two predilections came together as I considered how to build random encounter tables for a couple of campaigns that recently have been operating in urban areas; I hit the Dungeon Master's Guide in search of inspiration, starting with the material on pages 101-102. There are 25 suggested encounters in all, and unlike the sample encounter tables offered earlier in the same chapter, all of which are intended for wilderness environments, the urban encounter table doesn't run to entries that can be summed up as "1d2 locust swarms, average EL 5."
Instead, it helpfully suggests things like, "Contest in progress," and explains that, "[t]he characters are invited to participate in or judge a contest of some sort. The match could be anything from a foot race to an intellectual test to a drinking competition." Several of us have seen what this might look like in practice, as MinusInnocence's 2EE campaign featured a drinking contest that Thunk and Jugg'r participated in. I don't know enough about his DM preparation habits to be sure whether he cooked up rules for that, or found some online, or just made something up on the spur of the moment. And I don't know if he generated it from a random encounter table or not, although it's pretty clear he uses random encounters to some degree. But I fancy that it was an interesting challenge, and it led to some entertaining roleplay.
But the "contest in progress" option is only one of 25 suggestions, and in all honesty it is one of the more concrete ones. I'm struggling with one of the others in particular: "Spell gone awry." The descriptive text: "A spellcaster has foolishly experimented with a spell or had a mishap with a scroll. The PCs might have to content with a rampaging summoned creature, the aftermath of a fireball in the marketplace, or a squad of the city guard under a confusion effect."
I don't really like the idea of using a scroll mishap as the basis for this encounter, because most of the rules pertaining to scroll mishaps (see http://www.d20srd.org/srd/magicItems/scrolls.htm) are delineated in terms of minor variations on the effects of a spell. It works out pretty well if you assume that a spellcaster has somehow botched a fireball or confusion in such a fashion that it turns into something that would come to the attention of a group of PCs. But you have to pile caveat on top of caveat to get to that point. The spellcaster has to:
- miscast a spell from a scroll,
- without knowing it, or
- in a setting where it immediately can affect bystanders
It requires a lot of coincidences all in one place, in order words. That's okay if you're building a random encounter that's only good as a one-time deal, I guess. But if this kind of thing happens on a semi-regular basis, then it'd require explanation within the larger framework of the campaign setting. Magic users would be subject to extreme suspicion and hatred. Governments would seek to regulate them, and scrolls in particular would be heavily controlled or even outlawed because they represent a genuine public safety issue, on par with what might happen if people were cooking up nerve gas or napalm in their kitchens at home.
Basically, I feel like it works if your players aren't the type who ask questions about weird things that go on in the game. But if verisimilitude and logical consequences are important to you and your players at all, it's a problem.
And furthermore, if I'm going to build an encounter that's only good as a one-time deal, I'm going to build something that's intended to spawn a side quest of some kind, and it's troublesome to try to do that from the starting point of, "some dumbass was fooling around with magic he didn't understand and couldn't control." So at least for the purposes of generating a relatively closed-ended random encounter, I think it's probably the case that it's best just to forget about scroll mishaps and behave as if the "Spell Gone Awry" category is by default the result of some kind of failed experiment or ritual. If we take that approach, then a few options pop out at us right away. They aren't necessarily mutually-exclusive. I think it's also important that all of these options inherently provide for a Challenge Rating or Encounter Level.
I guess this probably is the most obvious variant of the encounter; it's literally the first suggestion offered by the descriptive text, and it's also a good model for the proposition that spellcasters who meddle with extraplanar beings are especially dangerous and/or foolish. As I see it, the starting point for a failed spell experiment is pretty straightforward, because the Dungeon Master's Guide offers guidelines on how long, how much it costs, etc. for a PC to research an unique new spell. So all we have to do is accept that if PCs can do that, so can NPCs. And then the next step is to say that an NPC happens to have been experimenting with some new kind of conjuration (summoning) spell. From there, it's a simple matter just to ask ourselves, "what would I want to change about the existing summon monster spells?" Their shortcomings are mainly that it takes a bit longer to cast them, the summoned critters only stick around for 1 round/level, and the creatures summoned are selected from a defined list.
So if you're researching in this area, those would be the obvious things to try to improve on. Fortuitously, the summon monster spell chain would make the basis of a fine encounter if these spells had a duration measured in tens of minutes, hours, or days per caster level. And the creatures summoned provide a relatively good set of benchmarks for a wider palette of encounters. Maybe someone wanted a formian warrior instead of a yeth hound. They're about the same CR, have similar Hit Dice, etc. Whatever the exact motivation and choice of creature, it's pretty straightforward from a planning standpoint. The experimenter called up something that isn't under control and won't go home, and now it has gotten loose from whatever facility he was using as a lab. As long as you pick something that a spellcaster would reasonably want to summon by magic, you're basically good to go.
I've left off the "rampaging" part of the description here, because a lot of the options that could make their way onto the table are sentient creatures that may not default to violence. An otherworldly ant-centaur is going to be a disruption even if it's not hostile, and it'll draw attention and cause concern. There're grounds for the PCs to get involved. If they can figure out who summoned the creature, there's potential for a side quest that could establish either a friendly or a hostile relationship with that NPC, or with various authorities in the community. And best of all, from my perspective, is that the instigating event is by nature much more deliberative in nature. Someone didn't pick up a scroll and try to cast it when she should have known better. Instead, someone miscalculated a task that he believed was within the limitations of his abilities, and things got out of hand.
Out of all of the possible "scroll mishap" options, the "rampaging summoned creature variant" of this encounter probably is the easiest one to render as a logical chain of events. An inexperienced mage (or cleric or druid) finds a scroll of summon monster, it gets out of control, and now there's an angry hellhound running through the streets, eating people.
The major obstacle to using this variant is that it can be difficult to assign a CR to summoned monsters that have a summon ability of their own (this is a factor for many demon and devil options), because these creatures are assigned CR based on their possession of that ability. There really isn't any reason that the botched experiment can't also remove this restriction, though.
Fear the Walking Dead
I guess this is another case where you can take either the "research gone awry" or "scroll mishap" path, but if it is a scroll mishap, you still have a pretty good chance that the (ir)responsible spellcaster behind it has had to plan in advance by obtaining a suitable corpse or corpses on which to cast the scroll's contents, which will be specific in terms of how many Hit Dice of undead it can create. To my sensibilities, this makes the backstory unacceptably complicated. If you're not adhering strictly to Core material, then there's a set of summon undead spells that will do as an alternative, but at that point it's really just a variant of summon monster.
It gets more interesting if you posit that a more experienced necromancer was experimenting with animate dead; recall that this spell is permanent, the resulting undead are under the caster's control, and there are clear limits as to how many the caster can control at one time. The more rules govern how a spell works and the better defined those rules are, the easier it is to meddle with the spell in a way that makes sense when the PCs ask what went wrong.
The Core Rules don't offer variant skeletons or zombies; both of these creatures are templates themselves. But Libris Mortis does offer variants, and this is a good way to introduce that material into a game. The same book also offers a variety of feats that modify the performance of undead created by people who have them. If the experimenting spellcaster lacks the requisite feats for what he's trying to do, then that may be a good basis for a mishap as well.
Another option is the create undead chain of spells, which generate intelligent undead of several different types. And the creatures produced in this fashion are inherently not under the control of the spellcaster who made them. But it's not cheap to cast, so the proposition that someone is just going to create a ghoul and then let it wander off to do whatever it likes is pretty small. If someone is prepared to obtain a corpse and spend 100 gp and an hour of valuable time turning it into a ghoul, he's also going to provide for some means of making the ghoul do as it's told; there are a couple of Core spells for this exact purpose, and they're of lower level than the create undead chain.
This one doesn't work plausibly as a scroll mishap variant for the same reasons that apply for animate dead, except even more so. But I think the biggest problem with the idea of undead creation gone awry is that it's implausible as a repeatable encounter because freshly created, uncontrolled undead are likely to turn on their creator.
On the favorable side, it's really easy to assign CR/EL to any of these.
The Eberron setting introduced a "living spell" template that embodies a spell of the DM's choice as a creature. In that setting, living spells hang around battlefields where a lot of magical energy has been unleashed all at one time, but there's really no compelling reason why an enterprising DM couldn't repurpose the template to a spell gone awry scenario. I think one of the late Monster Manual volumes also contains this template, too.
This option has several things going for it. Living spells are persistent creatures, and this is a big deal from a planning perspective because it makes life so much easier for the DM. You don't need the spellcaster responsible for the encounter to be in such close physical proximity to the encounter. And it invites some speculation about just what the spellcaster was really trying to accomplish. One option is that the responsible party was experimenting because of a desire to uncover the basis for an improved version of the Extend Spell metamagic feat, but it's also equally plausible that the goal of the experiment was to create living magic, and that the spellcaster simply wasn't prepared for how weird that would really be. This option also is attractive because it's extremely versatile. The living spell template is applicable to almost any spell, and CR/EL is built into the template.
Finally, there's the option of using a spell gone awry scenario as the pretext to dump some kind of supernatural hazard into a populated area. The Hordes of the Abyss supplement offers a few ideas along these lines (p. 112). Unsurprisingly, most of those examples are demon-themed, which imposes some requirements on the DM in terms of delineating what kind of NPC is responsible for the effect. Cityscape also offers a few that are more generic. Supernatural hazards like these are a lot of work to put together because they aren't really based on any defined subsystem of the rules, so you have to eyeball everything. But they also are really interesting and unusual, and they're something that I'd certainly be interested in including more of in my games. I'm just having some trouble coming up with ideas.