If a unit gains an Attack trigger ability (like from Recurve Bow via Angle Shot) after already being designated as an attacker, does that Attack trigger get processed?

Ruling: No, Attack triggers added after a unit has already gained the attacker designation do not trigger. The trigger condition requires the unit to gain the attacker designation while having the ability, not to gain the ability while having the designation.

Sequence:

• Unit is designated as an attacker
• Attack triggers on that unit process at that moment
• If the unit later gains new Attack trigger abilities during the same combat, those new triggers do not process
• If the unit leaves and returns to the battlefield during the same combat, Attack triggers still do not process again (they only trigger the first time a unit gains attacker designation per combat)

Nuances:

• This ruling applies specifically to triggered abilities (like Attack triggers), not passive abilities
• Passive abilities like Assault work differently - they only care whether the unit currently has the attacker designation, not the timing of when it was gained
• A unit can only trigger Attack abilities the first time it gains the attacker designation in a given combat