When are the possible scenarios during play when the game is in an open state where I could play an ACTION card?

Based on the rules of Riftbound, an Open State occurs when no chain exists (Rule 330.2). You can play an Action card during an Open State in the following scenarios:

1. Neutral Open State (Action Phase)

During your turn, when there is no showdown in progress and no chain exists, you are in a Neutral Open State (Rule 310.1).

• When: During your Action Phase (Rule 316.2).
• Requirement: You must have priority.
• Note: In this state, you can play Action cards, Reaction cards, or activate abilities (Rule 316.2.b).

2. Showdown Open State

A Showdown is a structured window of opportunity that occurs during combat or when a player moves to an empty battlefield (Rule 316.5).

• When: During a Showdown, provided no chain currently exists (Rule 310.3).
• Requirement: You must have focus (priority).
• Note: According to Rule 316.5.c, a Showdown is a window where players may play cards and activate abilities with the Action or Reaction keyword.

Important Constraints to Remember:

• Actions cannot be played in a Closed State: If a chain exists (a "Closed State"), you cannot play Action cards. You are restricted to playing only cards or abilities with the Reaction keyword (Rule 309.1.a).
• Actions start chains: Playing an Action card in an Open State will immediately create a chain, moving the game into a Closed State (Rule 351.1). Because of this, you cannot "respond" to an opponent's Action card with your own Action card; you must wait for the chain to resolve and the game to return to an Open State (Rule 330.1.a and FAQ).
• Focus in Showdowns: In a Showdown, the attacker is granted empty focus first for the first chain. Focus only passes to the next player after a chain fully resolves and the game returns to an Open Showdown state (FAQ).

Summary: You can play an Action card whenever it is your turn in a Neutral Open State or whenever you have focus during a Showdown Open State.