If my opponent starts a showdown and I play Portal Rescue on my Brynhir during their turn, and they don't React to it, can my opponent play any cards for the rest of their turn?

Ruling: No, the opponent cannot play any cards during the rest of their turn if they don't React to Portal Rescue played on Brynhir Thundersong.

Sequence:

• Opponent starts a showdown
• You play Portal Rescue on your Brynhir during opponent's turn
• If opponent doesn't React to Portal Rescue
• Opponent cannot play any cards for the remainder of their turn