Once Incapacitated, AZ offers the ability "Choose a hero. Increase the next damage dealt by that hero by 2" (paraphrasing from memory). If he chooses Tempest, and Tempest uses his Squall power to deal 1 damage to every non-hero target, that's all simultaneous right? So each target would take 3 damage instead? Or do you have to pick one of them which takes the "first" damage, and only that one goes up by 2?
Next is just the first instance of a multi-target attack. Hasty Augmentation in Unity's deck is an example of wording that increases all instances of damage from an attack
So if it's all simultaneous, do you just pick which one to consider "first"?
It's not simulatenous, nothing in Sentinels is simultaneous. What you have is an attack that hits x targets, you pick the order that those targets are hit in. So for the damage bonus pick which target you wish to hit first and that damage gets the bonus, everything else gets the 'standard' damage.
Any action from a single card or source that effects more than one thing that would seem to be simultaneous is instead resolved in the order the heroes choose, so Tempest would choose who to hit first, and that hit would be at +2 damage.
If multiple cards activate simultaneously the order is in card play order.
I would have done that wrong.