When in a player window where triggered abilities can take effect, how do players determine the order of execution of the triggered abilities? Can they be in any order, i.e. player 1 triggers 2 abilities, then player 2 triggers 1, then player 1 again triggers 1? Or do they follow certain restrictions such as particular abilities requiring all triggerings for that to be done atomically or, in the case of a disagreement among players, defaulting to the player who controls the lead investigator to decide who goes when, or in player order etc.? I would think the answer is likely in the order the players decide, with disputes resolved by the lead investigator.
Form Rules Reference, p.17
Priority of Simultaneous Resolution
If an effect affects multiple players simultaneously, but the players must individually make choices to resolve the effect, these choices are made in player order. Once all necessary choices have been made, the effect resolves simultaneously upon all affected entities.
- If two or more forced abilities (including delayed effects) would resolve at the same time, the lead investigator determines the order in which the abilities resolve.
- If two or more constant abilities and/or lasting effects cannot be applied simultaneously, the lead investigator determines the order in which they are applied.
If multiple triggered abilities trigger at the same time by the same player, those abilities can be placed onto the stack in the order of that players choosing resolving in reverse order. If multiple triggered abilities from multiple players trigger at the same time, first the active player orders their abilities in the order of their choosing onto the stack, then the next player in turn order does the same for their abilities, going around until each player has done this. This is active non-active player order.
The abilities begin to resolve in reverse order one by one from how they were put on the stack (meaning the last ability from the player furthest from the active player would resolve first). If a triggered ability or abilities were to then be triggered during the resolution of one of the stacked abilities, the current ability would finish resolving first. Before the next ability on the stack resolves, the new triggered abilities would be put onto the stack in active non-active player order again, and the last of these added triggered abilities would be the next one to resolve.