Thor of Higher Avalon: Fighting Dissidents reads "While Thor of Higher Avalon is Active, at the start of your opponent's attack step, deal 2 damage for each Team Affiliation in their Field Zone, divided any way you choose among their characters."
Does Thor's ability trigger....
A - When the opponent says, "I'm moving to the attack step," or otherwise indicates that they are not ending their turn after Main Step, which means Thor's damage happens before opponent chooses any dice to attack? or
B - The moment the opponent chooses a die to attack, which means the opponent's "when attacks" abilities will happen before Thor triggers?
Thank you!