Call of Cthulhu by Chaosium is one of the classic skill driven RPG systems out there, using a percentile system that can be found in the family of games that includes Stormbringer, Ringworld, Runequest, and others spawned from the same core Basic RPG (link to Basic RPG). The most recent 7th Edition of the game has continued with the core, fine tuned bits, and added some more options for play. One thing our table could not find within these rules (and not in a quick scan of previous editions either) was a decent means of resolving one character helping another in a skill check.

In a game that often depends on the Investigators working together else they be devoured alone, this was surprising. Sure, they had a passage about multiple characters working together to lift something heavy but not one on how the antiquarian could assist the librarian in finding that much needed clue to disrupting an occult ritual. Instead the offered mechanics is to let all Characters roll and as long as one of them succeeds, then there is a success. The next closest example would be in combat if a character has grappled another and a third character gains a bonus die to their attack against the grappled character, but for most skill checks that wouldn’t work.

When there’s something eldritch in your neighbourhood, who you gonna call?

Our Solution

A Character who has an applicable skill rating of at least half the skill of the lead Character about to roll, then lead Character gets a bonus die to their roll if this is a roll that can be assisted.

Why not have all the Characters Roll?

Sure, why not? The more Characters able to attempt a roll, the better chance of achieving a success.

That works fine assuming that there are no consequences for failures or other limiting factors on this skill check. However what about when there are penalty dice applying to the skill check or a hard (rolling lower than 1/2 your skill) or better result is needed or they only get one shot to get this right? Force hammering at the skill checks starts to lose out against gaining that bonus die. Outside of combat, not many mentions are made of how to get a bonus die so having one more way to get one seemed a good way to go.

So what about two or more Characters helping in a roll?

If you as the Keeper are comfortable with this being a skill that can be assisted by multiple characters, go for it (still with the limit of 2 bonus dice to any roll). At our table, we didn’t really have that come up often. Just keep in mind the probability shift from one bonus die (about +20%) to two bonus dice (about +30%) if I understand the math correctly …

Why we selected this mechanic …

First, we considered the Help action in Dungeons & Dragons 5E. Basically, if one character takes an action to help, it grants advantage (in this case roll an additional 1d20 and take the better of the two, or about a +4 equivalent according to the probabilities at play).

Applying that to Call of Cthulhu where you might get a characters with 0% or even a mere 1% giving a bonus die to the percentile roll felt wrong and way too easy for a game that has a reputation for devouring player characters and insanity. Perhaps if you wanted a more epic and pulp flavour, you might choose this, but we didn’t.

Then we looked at Pathfinder where one or more characters could assist by rolling a 10+ with that skill to give a +2 bonus to the skill roll by the lead character.

In Call of Cthulhu, unless there was a greater degree of success required* (see end note), if an assisting character made the roll, the lead rolling character wouldn’t need to make that roll.

If we flipped it, requiring that a more skilled character could without rolling, grant a bonus die to a less skilled character, it would really limit the action of helping someone else to someone of a similar skill rating. You might find this to be a solution for your table while your players attempt to crunch numbers to maximize their chances, but this was rejected by all the players at our table.

*A few definitions for those less familiar with the system

  • Skills – Range from 00% to 99%,
  • Success / Failure is measured by your d100 roll against your skill rating
  • Hard – Rolling equal to or less than half your skill ranking
  • Extreme – Rolling equal to or less than one fifth your skill ranking
  • Critical Failure – If your skill ranking is equal or greater than 50%, you only critically fail on a 00%, otherwise your critical failure range is 96-00% (with some exceptions with in combat)

At initial character creation, these numbers would be recorded on your character sheet and there was a handy reference table in the handbook and the Keeper’s screen for the math adverse.

*Older editions used a really simple mechanic for determining if you rolled a critical – if you rolled a 0 or 5 on the ones die of your percentiles, it was a critical. Success or failure depending on rolling equal to or less than your skill rating (i.e. if you had a Shotgun skill of 50% and rolled 45% , you had a critical success, but if you rolled 55% then you had a critical failure. If your roll didn’t end in 0 or 5, then you just had a regular success or failure). I really liked it for having the 20% chance of a critical baked into the roll without any other math involved. However, with more recent editions using 3 degrees of success (extreme / hard / regular) that was no longer viable.

Just a little something extra …

Flesh Ward is one of those spells that will inevitably fall into your game. It is one of a couple useful ones that will help survival but it helps a little too much as the one character grinds through their sanity to buff a fellow character to being bullet proof. My solution – inflict Sanity cost on the caster as well as the recipient (assuming that the spell or ritual description doesn’t already have a Sanity cost for additional characters involved in the casting). This is a genre where everything should have a cost.