Can you play a hidden card (like Consult the Past) from Battlefield B during a showdown on Battlefield A, and can you play it during your turn without any showdowns or chains happening?

Ruling: Yes to both questions. You can play a hidden card from Battlefield B during a showdown on Battlefield A, and you can also play a hidden card from Battlefield B during your turn without any showdowns or chains happening.

Nuances:

• The card must have been hidden on Battlefield B in a previous turn