A mechanic to resolve multi-stage, multi-participant tasks

Question

Sometimes the party wants to complete a multi-part task where the performance of one of them on one part can help or hinder the performance of another one on a different part. They have a common goal, but are involved in separate and discrete parts of the task.

For example, in one game I DM'd, an invisible party member entered in a busy public square and needed to attract the attention of another party member. They knew the second party member was close at hand, but did not know exactly where they were. I had them roll Intimidation(Charisma) for how loud they could shout, and had the other PC roll Perception(Wisdom) for how well they could pick out the shout against the background noise of the city. With the overall goal being to convey the message, the better the first PC performed on their part, the easier the part of the second PC should be.

Now, I could have just had the second PC roll Perception with advantage due to the assistance of the first PC, as in the rules for Working Together. However, this was unsatisfying to me, because it would have the first PC provide a 'static' bonus without accounting for how well they did on their part of the task. It also goes against the requirements of the 'Working Together' rules themselves, which state:

A character can only provide help if the task is one that he or she could attempt alone. For example, trying to open a lock requires proficiency with thieves' tools, so a character who lacks that proficiency can't help another character in that task.
Moreover, a character can help only when two or more individuals working together would actually be productive. Some tasks, such as threading a needle, are no easier with help.

Even though the PCs had a common and interdependent goal, the first PC can't really help the second one listen, and the second one can't really help the first one shout.

I could also call this a group check:

When a number of individuals are trying to accomplish something as a group, the DM might ask for a group ability check. In such a situation, the characters who are skilled at a particular task help cover those who aren't.
To make a group ability check, everyone in the group makes the ability check. If at least half the group succeeds, the whole group succeeds. Otherwise, the group fails. Group checks don't come up very often, and they're most useful when all the characters succeed or fail as a group.

While the PC's certainly are trying to accomplish something as a group and those who perform better are 'covering' those who do not, this misses the point by having everyone involved roll on the same skill when in my example they are using completely different skills to achieve different parts of a task.

At the time this event played out, I just had each of them roll, with the result of the first roll vaguely informing me of the DC for the second roll. I would like something a little more formal, however.

I am thinking that what I could do is set an 'overall' DC for the task and double it. The result of the first PC's roll would then reduce the DC of the task for the second PC.

For example, if my overall assessment of the DC for the task (hearing the shout) was 'Moderate' (DC15), then the combined DC would be 30. If the first PC rolled a 10 for their Intimidation attempt, that would reduce the DC by 10, such that a not-very-impressive shout meant that the second PC needed a DC20 Perception check to hear it.

I'm interested in an evaluation of this proposed mechanic. If you think this type of situation is covered in RAW, then please explain how. If you think it is not, please keep in mind good subjective as applied to homebrew review questions - a good answer should describe actual experience with trying to accomplish the same goal that I have, even if the mechanic to achieve it was different. Also, an objective assessment of the numerical consequences of such a mechanic (how it compares to a single skill check, to the 'working together' rules, to 'group checks', and how it is different from 'rolling to failure') would be welcome, even absent experience in implementing something like this.

Answer 1

I think this is elegant but very tough

My first observation is that when you multiply the base DC with the number of contributors¹, having more helpers does not make the task easier. So this mechanic only applies to tasks that need all contributors, not to tasks that get easier the more contributors you have.

My second observation is that you are trying to achive two different things:

1. combining different skills in a common task
2. finding a different mechanism² to combine the contributions in a common task

You can actually look at these separately:

Combining different skills

All of the book options assume characters use the same skill to help with the outcome of a DC challenge, there are no "mixed skill" DC checks in the game, even though there are challenges conceivable (as in your example) where it might seem plausible. I think such situations are not common, but the simplest way to handle them would be for the DM to allow using the specific needed skills that can reasonably contribute in the Help Action or the Group Check option, on a case-by-case basis. No new mechanism for combining them is needed.

Your new combination mechanism

For the following discussion, let us assume you allow combining different skills with the book mechanisms, so we can compare them to your method (as the book mechanisms do not allow combining different skills, there otherwise would be nothing to compare):

• Help action: helpers grant advantage to the one character rolling against the DC. There is no benefit to having more than one skilled helper because multiple instances of advantage do not stack to add more dice to the roll. The helpers do not need to roll anything. This grants better chances for success to the characters than your mechanism, because they can chose the one with the highest bonus to lead the roll, the lower bonus of the other will not detract, and that character receives advantage. Even in the fringe case where all characters have the same bonus on their skill, this would be easier to achieve than in your system, due to the advantage (with higher variance, as there is only one roll).

For example, imagine the DC is 15, and you have two characters A with +4 on intimidation, B with +2 on perception. Then with the Help action, A gets to roll with advantage, with 75% chance of success. In your system, the combined DC would be 30, and the expected chance to achieve this (if my anydice got this right) is only 38.25% -- which intuitively makes sense - the average for each of their rolls would need to be higher than the expected 10.5, for 2d20 + 2 + 4 to be higher than 29.

• Group Checks: everyone makes a check, if at least half succeed it is success, otherwise failure. Here, the more skilled participants you have, the better. Again, success is easier than in your system, as only half of the group needs to succeed. In your system, on average, everyone needs to succeed.

In our example, at DC 15, A has a 50% chance of success, B 40%, so the group check has a chance of 70% success, as it is sufficient for one of them to succeed (they fail if both fail, which happens 50% * 60% = 30% of cases). For your system, they need to get 30 or better with the sum of 2 rolls. Again, the chance for this is 38.25%, so again, your system is a a lot harder than a group check.

• Rolling to failure: this means, everyone has to make their normal check to succeed, if one fails, all fail. Your mechanic is more forgiving than that. Even though all on average need to beat the DC, no single failure knocks out success entirely. Rolling to failure is taking the #2 spot on the Alexandrian's "DM Don't" list, for a reason.

In our example, the chance of both characters succeeding on the check is 50% * 40% = 20%, which is much lower than the 38.25% from your mechanism.

Conclusion

The proposed mechanic is very elegant, but at the same time significantly more difficult than comparable mechanics the game already offers. You could try to address this by coming up with more complicated ways to set the "combined" DC, but I think this would quickly get clunky, and also may be hard to balance across DCs and numbers of participants.

In my mind, allowing different skills with the established mechanisms is more in line with the design spirit of 5e, than introducing a degrees-of-success mechanic for a corner case situation.

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¹ I am assuming you set a DC for a given task depending on difficulty using the normal difficulty tiers, which you then multiply with N, the number of characters involved, for the overall DC. Your example of N=2 is the case where only two characters work together.

² By default, the game has no concept of degrees of success or failure for skill checks, it is binary, either you succeed on the check, or you don't. The DMG on p. 242 proposes "flourishes and approaches you can take when adjudicating success and failure to make things a little less black-and-white", including Success at a Cost ("Failing Forward") , Degrees of Failure, and Critical Success or Failure, but not something that in general allows degrees of success with increased rolls above the target DC. So your system is fundamentally different in this regard.

Answer 2

I don't think this does what you want it to do.

While there is precedent for adding up many participants' rolls towards a cumulative DC, the place where that really makes sense as a mechanic is when you're going to offer tiered results, with DCs that might be otherwise ridiculous but make sense when there's three to five people contributing.

For example, after a shipwreck, you might have everyone roll Survival, and have a list of what they can get done before dark with that cumulative roll. Say, for an aggregate 20, they can construct a basic shelter and a small fire. For a 25, they are also able to gather enough food and water for the group's needs. For a 30, the shelter is more comfortable, with makeshift walls and bed-mats. For a 40, the shelter is also surrounded with triplines, giving the party advantage on any rolls to avoid being surprised in the night.

If you aren't going to offer a menu of results like that, then I'm not sure you're really getting anything out of that method over a simple group check (i.e. everyone rolls against the same standard DC and if at least half the party succeeds, they all succeed). In either case, good rolls can counteract bad ones.

But I wouldn't use any kind of roll aggregation for just two people trying to do a job together. If they really are contributing to the same task in different ways, just call it Helping and make a single roll with advantage to find out what happens. Generally a single task should have only a single roll associated with it -- if any at all.

Should you even roll for this?

And that's where I'm a little leery of the situation you described. You should only call for a roll when the situation is important and failure is consequential.

Now, I don't know your game. Maybe there was a story reason that "Can you get your friend's attention from across the square?" is actually going to matter, where you can't just keep trying until it works. But it sounds a lot like an inconsequential roll to me, and in that case there should be no roll at all -- the characters just meet up and move along to the next thing.

But again, even if there's something that makes this roll consequential, wrapping more mechanics around it than a simple ability check feels like overdoing things, in my opinion.

Verify range to target. One roll only.

If you need to roll it, my recommendation is to keep it very simple. Decide who's the more important element of this roll -- the shouter or the listener. This probably comes down to the characters themselves; if you have a huge barbarian yelling as loud as he can in the square, have him do the roll. If it's a keen-eared elf rogue being called, have them roll it. When I have questions like this, I will often just look at the two characters' stats and have the roller be the one with the higher bonus. Set the DC and call for the roll. You aren't trying to harvest an intact venom sac from a basilisk or sail a ship through a hurricane. You don't need to get complicated for this.

Coincidentally, for a sheer "how loud are you?" roll, I'd probably just call that a raw Constitution roll and be done with it.

Answer 3

Nothing is inherently wrong with this idea

You're essentially creating a higher than normal DC and having the players do a "combined check" to complete a task instead of a "group check". This would also work for a "good cop, bad cop" routine; Bad cop rolls for Intimidation and the good cop rolls Insight (being empathetic).

I do wonder about how you are arriving at the DC

I don't think that an arbitrary doubling of DC is the right move. Consider the "Setting a DC" table:

Difficulty	DC
Very Easy	5
Easy	10
Moderate	15
Hard	20
Very Hard	25
Nearly Impossible	30

Most tasks that would even require a roll will be Moderate or Hard. Which means the DC is always going to be 30 or 40. And if any aspect is Very Hard, then it becomes 50 and puts a lot of pressure on both parties instead of just the aspect that would be difficult. Throwing a lit torch to someone is easy, but catching it one-handed, the right way, is much more difficult.

In your example, yelling is not that difficult; ask any couple that's been married for a few years. But hearing and understanding that yelled message is going to be much harder; ask the other person from that couple. If not prepared to listen, picking out a single voice from a crowd (even a loud one) and understanding the message being yelled, is quite a feat. So it might be better to create a DC for each part separately, and then combine the two for a more varied total required.

And you take away some roleplay options

Say the yeller rolled very well, but the person they yelled to rolled poorly; combined they did not get DC 30. By combining the totals it is just a pass/fail (which is correct for skill checks). But if you keep things separate you can now run with "Character B didn't hear your message, but the local guard did and are coming to investigate." Or the opposite, "Char A tried yelling at the same time as some vender started their presentation to draw attention, so their message was lost in the din. However, Char B did recognize Char A's voice yelling something." Char B can now take action based on hearing "something" but no idea what the message was.

In the end; it may not help

The idea works better with characters both performing the same task; both using Strength to break a door, or both using Sleight of Hand to cheat the house at cards. It's pass/fail based on both efforts.

But when it's two characters performing two different tasks that just happen to have a common goal, it can break down. Not in a game breaking way, but in a missed opportunity and possible illogical DC standard.

As a DM, I've always ruled the way you initially did. It's two separate checks, but the success/failure on the first check influences the chances of the second check.

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Side note

In the given example, unless Char B was actively listening for a yell, they probably shouldn't have gotten a roll at all, but only used their Passive Perception value. So in this case, it would be Char B's PP then add Char A's Intimidation roll.