If Mask of Foresight is equipped to a unit that is assigned as a defender with another unit present, then one unit is moved away leaving the masked unit alone, does Mask of Foresight trigger?

Ruling: No, Mask of Foresight does not trigger. The trigger condition checks whether the unit is alone when it is initially assigned as attacker/defender at the start of combat. Moving another unit away afterward does not change the attacker/defender status or cause the trigger to check again.

Sequence:

• When combat starts, all units are assigned as attackers and defenders
• At that moment, Mask of Foresight checks if the unit is alone
• If the unit is not alone when assigned, the trigger does not go on the chain
• Moving units away later does not cause the trigger to re-evaluate

Nuances:

• Attack/defend triggers can only be fulfilled once per unit per combat
• If a different unit is moved onto the battlefield alone after the initial assignment (during or after the initial chain), that unit's Mask of Foresight would trigger
• The same unit cannot trigger its attack/defend ability multiple times in the same combat, even if it leaves and re-enters the battlefield