In an episode of Order 66, while discussing social checks, EOTE lead designer Jay Little made a reference to using Brawn as the characteristic for a Coerce check, for example if the character was flexing their muscles and using their size as the basis for the intimidation.

Are there any rules or guidelines for this kind of characteristic substitution in the rulebook?

I had a look through the Skills chapter and the sections on assembling a dice pool and I didn't see any. I just wanted to check and see if there was anything written down.

No that I can think of specifically saying "If you're not in the mood to use x, feel free to use y" but there's a few places where it does pop up (using cool or discipline for fear ect.)

There is a line in the description for Skulduggery that indicates that sometimes it will be used with Agility instead of Cunning. I tend to treat most such things as Coordination checks since I otherwise see that skill used only rarely.

I just wanted to check and see if there was anything written down.

The only place I can cite from the rule book is the sidebar on 237, where it talks about using Athletics for repairing hull trauma instead of mechanics. But basically it's implied that if you can justify that skill to the GM somehow, then it's a valid use. I would, under the right circumstances, allow Brawn for Coercion and the like.

Resilience always leaps to mind for me. In so many of the amazing survival stories it was clearly the will to live and overcome that made the difference and not any physical attribute. Willpower could, and probably should, be used in many cases for this skill.

I'd say that if the player can provide a really solid justification for using a different Characteristic for a skill (and you as the GM feel they're not trying to abuse the system in doing so), then let them do so.

2P51's got a point about Resilience being rolled with Willpower to reflect a "fierce will to live" even when the physical body (Brawn) has pretty much reached its breaking point.

I'd draw the line at combat skill checks though, particularly in trying to use Agility instead of Brawn with the Melee or Brawl skills.

One thing I liked about nWoD was the encouragement to use different characteristics as the base for a skill depending on the situation. There would be a default, but it's not always entirely applicable. Brawn for Coercion could certainly work, especially in situations where the Brawn PC is assisting the Face PC.

To HappyDaze's point, I wish they'd have lumped Coordination into Athletics, then let you choose Brawn or Agility as appropriate.

I could see using Agility for a melee or brawl check if it is applied to a martial art kind of check. Aikido, Judo and Wing-Chun are just a few general examples where the core principles behind the style are based on speed and coordination, even tactical foresight instead of physical strength or prowess.

In the case of melee, certain weapons could be seen as more finesse-oriented in combat applications. A fencing foil would be the best example off the top of my head.

I realize that the Brawl/Unarmed Combat rules are assumed to take in the vast majority of fighting styles (wrestling, martial arts/grappling and pugilism), but I would ask for/allow a PC to use Agility in the case of trying to perform a specific action that demands it as the core physical principle, or if the action was so specific and central to the structured gameplay/narrative.

Stating that they want to grapple, and flip an opponent into a submission hold or similar would probably require a combination of roles over a turn or two. Brawn/Brawl to grapple, or Agility/Brawl to use their weight/momentum against them to do a shoulder flip or similar. Possibly throw in an extra maneuver cost or something. Just spitballing.

Cunning could even be used in the case of trying to anticipate an opponents actions/tactics, perhaps to provide a boost or lowered/downgraded difficulty on the PCs next check. ie. make a Cunning/Brawl check this round to downgrade difficulty/add boost on the next round.

In the case of Skulduggery, I might make a character substitute Agility in the case of trying to do tricky maneuvers while not being noticed, or accomplish a risky task. I understand that stealth plays a role as well, so between Stealth, Coordination, Skulduggery, Brawn, Agiltiy, Cunning and Intellect, there are quite a few combinations that can all be allowed and justified in the RIGHT CONTEXT. Just because it applied in one given situation doesn't mean it should be house ruled for all scenarios.

That's why I would say that any arguments from either side of the screen have to be good ones, and should be part of the social contract that all players can agree to. If someone doesn't want that kind of dice pool swapping, follow RAW, or work something out.