Can you reveal a hidden card from a battlefield where a showdown is not currently happening (e.g., revealing 'Consult the Past' to draw during a showdown at a different battlefield)?

Ruling: Yes, you can reveal hidden cards from any battlefield whenever you have priority, regardless of where the showdown is happening. The restrictions are on how you can use the card, not on when you can play it.

Nuances:

• Some cards like Block may only target units at their own battlefield, but you can still react with hidden cards from any location when you have priority.