Can you use Flash on a unit at Battlefield A in reaction to an opponent's move to Battlefield B, then use Ride the Wind to move a unit from your base to Battlefield B when the showdown starts?

Ruling: You cannot react to a standard move with Flash because standard moves do not create a chain. However, once the showdown begins and you have focus, you can cast Ride the Wind to move a unit from your base to that battlefield.

Sequence:

• Opponent declares a standard move to a battlefield (cannot be reacted to)
• Showdown begins at that battlefield
• When you gain focus during the showdown, you can play Ride the Wind to move a unit from your base to that battlefield

Nuances:

• If a unit has a move trigger that creates a chain (like Traveling Merchant), you could react with Flash before the showdown begins
• Ride the Wind is an action spell, so you specifically need focus (not just priority) to cast it