If Azir, Ascendant attacks and then uses its ability to swap with Azir, Sovereign from another battlefield, does Azir, Sovereign trigger its 'When I attack' ability and bring sand soldiers?

Ruling: Yes, Azir, Sovereign becomes an attacker when swapped into the attacking battlefield and triggers its 'When I attack' ability, allowing it to move sand soldier tokens.

Sequence:

• Azir, Ascendant attacks and is designated as an attacker
• On attack and on defend timings occur
• Azir, Ascendant uses its ability to swap with Azir, Sovereign
• Azir, Sovereign arrives and becomes an attacker on cleanup
• Azir, Sovereign's 'When I attack' triggers, allowing it to move all sand soldier tokens
• Combat proceeds to showdown

Nuances:

• 'When I attack' triggers the first time a unit is designated as an attacker in that combat, which doesn't have to be when combat starts
• If you are defending, swapping a unit into the battlefield does NOT make it an attacker - you remain the defender until that combat ends
• All of this occurs during the showdown phase since the swap ability is used when the controller has Focus