Can a player wait for their opponent's spell chain to resolve, then play an action spell (Bullet Time) during the same Showdown?

Ruling: Yes, this is correct. A player can wait until their opponent's spell chain resolves, then gain focus and play their own action spell during the same Showdown.

Sequence:

• Player moves 2 units to battlefield with opponent's 1 unit, triggering Showdown
• Player passes without playing anything
• Opponent plays Zenith Blade and reacts to it with Shen
• Chain resolves
• Player gains focus and plays Bullet Time to kill opponent's board