What are other rules for combined effort skill checks when cumulative effort matters?

Question

According to the question Determining "level" of an NPC ally for purpose of budgeting encounter XP when one character helps another they can use the “help” action to confer Advantage on the roll. Additionally, when an entire group is pitted against another, the DM can do a “group check.” 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.

These make sense for some activities - but for activities where combined effort is additive these approaches seem unsuitable. This would be particularly true for activities involving strength such as:

• Tug of War: A “group check” implies that a team of two could evenly beat a team of 100 depending upon the average strength of dozens of opponents. Even applying Disadvantage doesn’t seem to reasonably capture the odds of the situation.
• Carrying a couch up a flight of stairs or lifting a portcullis: For one person it might be impossible - but with five people the task could become trivial.

What are Adventurers League rules when combined effort should give cumulative advantages not just offer Advantage or treating both both sides as equal?

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Additional Clarification:

Per the comment request below, the specific situation we are trying to solve is we are looking for rules that would cumulatively increase the PCs chance of success as each additional PC tries to lift a portcullis. There is a portcullis in a pit that traps a PC away from the rest of the party. One or more other PCs may jump into the pit to help lift the portcullis. We were expecting that there might be a rule somewhere where every subsequent PC simply adds their strength to the effort so that, for example, a DC30 portcullis could be lifted, but haven’t seen anything. The use of the “Help” action doesn’t capture the additive help of additional people beyond one. Additionally, using the “Group Action” rule also doesn’t help if the DC is above the capability of the strongest person.

Answer 1

If the odds are that stacked in favor of either side, don't call for a roll

The Basic Rules pg. 58 and Player's Handbook both describe ability checks with the following prelude (emphasis mine):

The DM calls for an ability check when a character or monster attempts an action (other than an attack) that has a chance of failure. When the outcome is uncertain, the dice determine the results.

When cumulative advantages stack that heavily against the player characters, the outcome is not uncertain; the player characters shouldn't succeed. So instead of letting them roll, just tell them that the task is impossible.

Similarly, if they have so many advantages stacked up on their side that it seems ridiculous that the PCs have a chance to fail, don't have them roll at all; just declare that they succeed. So in the case of your DC 30 portcullis trap, if you feel that the combined strength of the player characters is enough to lift the portcullis, then don't roll and instead declare that they succeed in lifting the thing.

In this way, you are only rolling for contests which are possible at all and don't have to worry about situations in which either PC success or failure is almost impossible to justify.

But what if their combined strength is only enough to justify a chance at success?

You may end up in situations, like the trap you describe, where the combined effort of every PC is enough to have a chance to succeed, but is not enough so that success is guaranteed. In this case, there aren't really many rules to help you. 5e is designed with simplicity at heart, so there are no rules for circumstantial bonuses. With that said, you are the DM and you have control.

In the same ability check section, the basic rules and PHB say:

For every ability check, the DM decides which of the six abilities is relevant to the task at hand and the difficulty of the task, represented by a Difficulty Class.

You are in control of the DC, and you get to decide what it should be. You can even decide to change it on the fly to make your game work for you. We essentially solve the problem in reverse. Instead of looking for rules to modify the bonus to the roll, we leverage the power the rules give us as a DM to modify the target number.

You have every right to change the DC to whatever value you feel is most appropriate.

For example, 5 people lifting a portcullis might not be impossible, it might just be hard. So you can adjust the DC down from 30 to ~20 (based on the chart on typical difficulty classes in the basic rules and PHB).

You can even choose values between these markers. So, the task might be more than medium but not quite hard. In that case, you can decide "five people makes this a DC 17 or 18, not a 30". And then you can use either one roll from one of the players (with or without advantage at your discretion) or the group check rules now that the goal is much easier for everyone in the party to make.

This is the approach I use the most often in situations like these and I firmly believe that it's much less of a headache than trying to deal with rules for circumstantial bonuses.

Answer 2

Your examples were all feats of strength, in that case...

Groups Don't Roll

In Tales from the Yawning Portal, particularly the Hidden Shrine of Tamoachan section, there are few places that require feats of Strength. Instead of leaving it to the randomness of the dice, it is simply a matter of brute force. Rather than calling for a roll, they simply look for a total, summed Strength score - values from 20 to 50 are used.

The tomb lid can then be opened the rest of the way by the combined effort of one or two characters with a total Strength of 20 or higher. (TYP:HSoT, room 7)

This would take two average characters (STR 10+) or one extremely strong character (STR 20).

The block can be pushed back up the rollers by the combined effort of up to four characters with a total Strength of 45 or higher, or moved out onto the bare stone floor by the combined effort of up to four characters with a total Strength of 50 or higher. (TYP:HSoT, room 21)

This would take four characters of above average might (STR 13+), or some particularly powerful characters (STR 16+) in concert with a few lesser beings (STR 8+).

A more median requirement, around 30, would take two strong characters (STR 15+), three more average characters (STR 10+), or four relatively weak characters (STR 8) to do it.

Single Characters Roll

In the same content, there are a number of DC-based Strength (Athletics) checks, again for lifting. They are all instances where it's expected a single character can successfully accomplish the task. The rules for Help potentially allow a second character to get in on the action, but that's it. In most cases, further characters would just be in the way.

Answer 3

One official implementation you may be looking for comes in Tales from the Yawning Portal.

In The Hidden Shrine of Tamoachan there are instances where passing a check requires combined strength scores.

From page 67, regarding a large block obstructing a passage:

...the block can be pushed inward by the combined effort of up to four characters with a total Strength of 48 or higher.

And on page 68, regarding a stone slab covering a tomb (after unlocking it):

The tomb lid can be opened the rest of the way by the combine effort of one or two characters with a total Strength of 20 or higher.

In these examples rules for participants are set. How many characters can reasonably assist in the check? In a confined hallway 6 adventurers pushing on a door would probably be impossible (really the ones in the back are just pushing on the ones in the front).

It can be assumed that PC's will repeatedly attempt a task and this method takes in combined efforts and sets it to a simple pass/fail check. Either they have what it takes or they don't.

Answer 4

I cannot recall any official rules that would handle "cumulative" situations such as you describe, at least not in the core rules.

As a DM, I would probably just try and come up with an on-the-fly house rule. The easiest thing would be:

1) If the two sides are clearly uneven such as your 2 vs 100 tug-of-war then I would just call it and not bother rolling (unless 2 giants vs 100 pixies!)

2) I would still just use the group skill but alter the DC in some common sense fashion.

Examples:

In the tug of war, set a base DC, but the DC would increase by +2 for each extra medium creature on the other side or +4 for each extra large/super-strong creature etc.

For the portcullis, the base DC would be high enough that only a super-strong character stood a chance of lifting it alone, but each additional creature, if they succeed on their own DC 10 'assistance' check, would lower the strongest character's DC by 2.

This is all just opinion though. A DM could adjust the rules to be as simple or complex as necessary as long as it keeps the game moving forwards.