When Yasuo Remorseful attacks with a 'when I attack' trigger, does the trigger resolve before the Showdown begins, and what speed of cards can be played in response?

Ruling: When Yasuo attacks and his trigger goes on the stack, you have priority and can play Reaction speed cards (but not Action speed cards) before the trigger resolves. After the trigger resolves, you gain focus and priority to play Action/Reaction speed cards during the Showdown.

Sequence:

• Move Yasuo to occupied Battlefield, initiating a showdown
• Yasuo's attack trigger goes on the stack. You have priority
• When you pass, your opponent has a chance to play Reaction Spells
• Yasuo's ability resolves if you both pass priority
• You now have focus and priority and can play Action/Reaction spells

Nuances:

• You can 'hold priority' to play Reaction speed cards before passing
• This allows you to pump Yasuo's Might (e.g., with Discipline) before the attack trigger resolves