DC to solve a puzzle

[TheGogmagog]

The situation is our party came up with a puzzle for the BBEG. The DM knows how we did it and approves doesn't want to arbitrarily assume the BBEG figured it out. Hence the need to set a DC for those of you who read the title and thought it shouldn't be a skill check but role played.

Bestt case I'm thinking: The PC's spent a day figuring it out (similar to taking 20 to the Intelligence check). Four PC's contributed +2 aid another three times, plus the leaders Intelligence bonus. This would max around DC 28 intelligence check.

I can't recall the DMG suggested DC's, but DC 30 skill check sounds like a good nigh-impossible task. I also seem to recall a suggestion of DC 15 when you don't know what to set. I believe there is also a rule that 'usually' only two people can aid in a task, but that's how many players contributed to the solution so I'm thinking this would be a fair to assume the PC's also contributed. With the reduced starting DC 15, the result would be DC 23. A respectfully clever trick.

The PC's pulled the trick on the BBEG once, and needs to do it twice more. I figure it would be fair to get a +4 modifier after he sees the trick the second time.

 

[ThirdWizard]

Does the BBEG have henchmen? Does he have time? If so, he could probably take a 20 with several Aid Anothers as well, so that the DC isn't actually that impossible.

 

[TheGogmagog]

I'm not concerned what the BBEG's skill check is. I'm concerned about what the DC is. Also you generally can't take 20 on a knowlege check you either know it or don't. Which is why I also considered the arbitrary DC 15 for setting the trap. I suppose I could roll a D20 and add modifieres, but if the result is 11, then our idea wasn't that clever. Or we could add a situational modifier (+4 if the DM thinks it's a really clever idea) and then roll. We might end up at DC 13 or 32, perhaps our solution was obvious considering our resources etc.... The thing is the DM just isn't sure how to handle it. (his PC is down and I told him I'd check the boards).

Since I'm not getting any response here's a specific example. It involves a few DM rulings as given that might not be RAW, that I don't want to discuss. A person must pray at a holy site for 8 hours, the BBEG just has to show up and interupt the person to waste his attempt for the day. After the first attempt was broken we went to the site and cast an extended rope trick. A new addition to the party goes into the rope trick, pulls the rope in and begins to pray. The house ruling is that the rope trick counts for this prayer/ritual (don't bother arguing this point). It is also visible only with see invisibility AND the window has facing (not visible from the back at all). The BBEG probably had see invisibility, but was definitly was on the wrong side of the trick.

So, when he disrupts everyone in our party and the ritual is still complete, the most obvious conclusion is there was someone else there that he couldn’t see. There are dozens of ways of achieving this. Most directly invisibility and risking the area of effects (fireball cloudkill) disrupting the ritual. Perhaps an extended reduce person hiding within the area and under total concealment (under a bucket or something). Burying someone with a reed to breathe, and so on. The BBEG is surely smart enough to come up with ONE way to achieve the trick. What would the DC be to figure out what method we figured out?

 

[James McMurray]

The DC for figuring out which one you did is somewhere around infinity unless he has divniations. The DC to figure out a bunch of options, one of which is yours, is much lower.

I'd have him roll spellcraft at DC 20 and each amount over the threshold is one spell level he examines for possible solutions. Hitting DC 23 would let him know that rope trick would have worked, but also that invisibility was an option. I'd then take that information and compare it to what the guy knows about the party to see if he can reason it out any farther.

 

[Nail]

I wouldn't set a DC at all.

There are any number of ways (as you've mentioned) for your guy to be hidden but not be invisible. Practicly ALL of them involves a spell.

So the bad guy's solution? Cast Dispel Magic. Alot.

 

[Roger]

I'd do it a different way -- make it an Opposed Check. Basically "Puzzle Building" versus "Puzzle Solving."

What skills or abilities you actually want to use for those two things are up to you. The most straightforward might be just straight Intelligence checks, but there's lots of others that could be justified.


Cheers,
Roger

 

[ScipioX]

I'd have him roll spellcraft at DC 20 and each amount over the threshold is one spell level he examines for possible solutions. Hitting DC 23 would let him know that rope trick would have worked, but also that invisibility was an option.

That seems awfully high. Low level spells that are 'commonly' used, like invisibility probably shoudn't even require a spellcraft check to realize that it might pose a problem. Now he should make a spellcraft check to know what the duration of invisibility is, which would enable him to discount that method.

He should make a spellcraft check to know about rope trick, since its not used nearly as often, by either PC's or monsters. Probably 10+ level to be aware that it exists, and 15+level to know the specifics of its operation.

Assuming he makes a spellcraft check, then he will be aware of a variety of options. Depending on his wis/int, he will try and counter those that he thinks up.

In any case, its definitely not a puzzle for him to solve with an opposed intelligence check. The PC's didn't really create a puzzle, they just used a normal spell.

 

[SlagMortar]

I would have the DM come up with a list of as many ideas as possible to explain what happened. Then I would think of different ways to investigate a bunch of them.
1. Bring in creatures with scent and/or rangers to search the area for tracks.
2. Cast detect magic over the area.
3. Walk around the area with see invisibility
4. Send a bat familiar flying through the area with blindsense.
5. Cast some random area dispel magics to cover things he hasn't thought of.

 

[TheGogmagog]

Thank you all for your input, quite a bit to consider.
As I feared in the first post, a lot of the answers focus on the example instead of a general rule to follow, but it does keep the thread active. While the actual solution involved a spell, it involved a divine spell and the BBEG happens to be arcane, but I don't want the method used to resolve around these details. So I'm opposed to using knowlege arcane or spellcraft alone to resolve the trick. Besides that the spell is only a small part of the trick though, and Its possible to have been done without magic at all though, just the right ally to start with. I suppose the rope trick and other examples I came up with were a red herring that lead people to the 'straightforward use of spell' line of thought.

So far I'm thinking the opposed check is the way to handle this. In a non-existent skill puzzle solving (so Intelligence check). With synergy bonuses for the relevant skills, +2 for spellcraft, +2 for knowlege Arcane, +2 for knowlege planes, +2 for rope use, +2 for aid another and so on.

 

[TheGogmagog]

I would have the DM come up with a list of as many ideas as possible to explain what happened. Then I would think of different ways to investigate a bunch of them.

I like this process too, then the DM could roll randomly to see which one he investigates first in the event time is a factor (like he has x number of minutes of invisibility to investigate). With the exception of the ones that take no further actions, like bringing dogs.

[Issue resolved edit] The DM had come up with some DC and rolled in private. He botched both rolls (typical of him). So it all ended in our favor. He did come and try to foil a few of the possibilities but not the one we came up with. [Thanks for your input!]