Can you target a unit that is not at the active showdown (e.g., using an action card like Challenge to make a unit from a different battlefield fight a unit at the active showdown)?

Ruling: Yes, you can target units that are not at the active showdown with action cards.

Nuances:

• Cards played from hidden can only target units at the battlefield they were hidden at
• Units from different battlefields can be made to fight each other using action cards