When conquering on an open battlefield, can the opponent play action cards, or only reactions?

Ruling: Yes, actions can be played when conquering on an open battlefield. Additionally, all players are considered relevant in the case of an empty battlefield.

Nuances:

• Both actions and reactions can be played in response to conquering on an open battlefield
• If a unit enters an open battlefield and is removed (e.g., by Gust) before resolution, the point is not scored