When a Showdown is on Battlefield A and you have hidden cards on Battlefield B, can you react with those hidden cards, and what are the targeting restrictions? Can Tideturner be played from Battlefield B to affect units on Battlefield A?

Ruling: You can react to a Showdown on Battlefield A with hidden cards from Battlefield B, but you cannot choose units on Battlefield A with those spells (only units on Battlefield B). Tideturner is an exception due to errata and can be played from Battlefield B to affect units on Battlefield A.

Nuances:

• Tideturner has specific errata that allows it to work across battlefields unlike other cards