OK so title states the question but for a little more detail in what I am after, when firing with the auxiliary arc, using Backdraft does his ability add the crit result before AC would be used or after. Or would AC on Backdraft guarantee Hit, Hit, Crit?

Edit: Or I may have just answered my own question with the whole "dice can not be modified again this attack" part of AC. Grrrr still not 100% sure.

You can actually choose the order, because they are simultaneous effects controlled by the same player.

So, if you use Backdraft's ability first, you get (something) + 1 crit. The AC cancels all that and you end up with two hits.

If you use AC first, you cancel everything and end up with two hits. Then you can't modify again, so Backdraft's ability does nothing.

Either way, the combo is dead on arrival.

It would be after the Dice are cancelled/2 hit results are added, which you can't do due to the wording of accuracy corrector.

Yea, I figured it would be broken to work that way.