Third-edition Dungeons & Dragons introduced the aid another action and rolls to assist a character making a check. This mechanic carried into fourth edition and Pathfinder.
Typically, in a role-playing game, the game master tells the players when to make a check. For more, see “When should a game master call for a check?” Ideally, rolls to assist with a check should work the same way. When a player describes actions she takes to help, the GM should ask for her to contribute an assist check. For example, when Jasper the rogue tries to convince blind Auntie Fears that he’s a member of the Family, his player rolls the bluff check. If Astrid whispers Family lore in Jasper’s ear, the game master asks her to make a check to assist.
Too often, rolls to aid another come when the players ask to make the roll. The GM tells a player to make a check, and then everyone at the table, and the pizza guy at the door, all start rolling to assist. Everyone has lost immersion in the game world and turned to wringing plusses from the rules.
Assist with specific actions
When someone asks to aid another, as the game master, you should ask, “How do you assist?”
Sometimes the answer may be obvious. If a boulder blocks the tunnel, the more muscle, the better. Sometimes, the answer requires some ingenuity, so the players need to explain what actions they take to help.
Limiting who can assist
In many situations, not everyone can crowd in to assist. If the whole party wants to smash a ordinary-sized door, they will need battering ram. Even in role-playing tasks, you can limit how many characters can plausibly help. No one wants to enter a car dealership and be swarmed as every salesperson pushes to assist the sale. Ye Olde Wagon Shoppe is no different.
Assisting in role playing scenes
In role-playing situations, you will typically talk through an interaction that leads to a check. If someone wants to assist with the diplomacy, intimidation, or deception, they must speak up and contribute as the scene plays out.
For example, when Jasper bluffs Auntie Fears, you would normally role play the scene and then ask for a check to decide if Auntie is fooled. If Astrid wants to assist by whispering background to Jasper, she must help during the scene. Once you call for a check to find an outcome, she cannot interrupt and declare that she assisted retroactively.
Aid another may demand a different skill
Players take specific actions to help, so their aid-another checks depend on the actions they use. Just because Jasper makes a bluff check doesn’t mean Astrid rolls a bluff check too. Astrid might need to make a history check, or depending on Auntie’s family business, a streetwise check. If Astrid draws her knowledge of Family lore from the diary she read after the last scene, she might even assist without a roll.
Look for chances to grant an assist check
Sometimes when players become totally immersed in the game world, they will act to help, and then forget to lobby for an assist check. Ask them for the assist check. Everyone wins when players act in the game world and you can reward them for it.