I'm playing Brielle who has an ability to bury a card to add a d12 to her charisma check. Is it permissible to use this ability for a Diplomacy check? It seems like it should but then could you apply the same principle for a strength/melee or dexterity/ranged with some allies (provided it doesn't specify non-combat, of course).
If your character has the skill Diplomacy: Charisma +X, then all of your Diplomacy checks are also Charisma checks. This means things that impact Charisma checks can also impact Diplomacy checks.
If your character does not have that skill, then Diplomacy checks are not also Charisma checks so the above would not work.
Okay, that is very helpful and what I thought but wanted to be sure!