If a unit is moved into an already ongoing showdown (after the attack has started), does its 'when I attack' trigger activate?

Ruling: Yes, 'when I attack' and 'when I defend' triggers will activate if units are added to an already existing showdown. These triggers function as 'when I am designated as an attacker/defender' which happens during cleanup whenever combat is present.

Nuances:

• 'When I attack' creates a trigger that goes on the chain at the moment of attack
• 'While I am attacking' is a passive effect that is active at all times the unit is an Attacker and does not use the chain
• Cleanup happens frequently throughout the game, such as when an item is removed from a chain