When does Mask of Foresight's ability trigger, and does it trigger again if a unit becomes alone later in combat?

Ruling: Mask of Foresight triggers when a unit is first marked as attacker/defender and is alone at that time. It does not trigger again if a unit becomes alone later during combat.

Sequence:

• The ability triggers at the moment a unit is marked as attacker or defender
• This happens before passive stat increases
• The buff persists until end of turn once granted

Nuances:

• If your lone attacker/defender is removed from combat and then you move something else in, the mask triggers for the new unit since it is marked as attacker/defender and is alone
• If two units are defending together (like on Reavers Row) and one is moved back, mask does NOT trigger for the remaining unit because it was not alone when first marked as defender
• If a unit is defending with a hidden unit and the hidden unit is revealed, mask does NOT trigger again even if one dies, because the trigger only happens when first determined as defender