Can I cast a reaction (En Garde) as my opponent passes focus in a showdown, without actually receiving focus yet, and then doing nothing and passing focus when it is given to me so that the showdown resolves immediately?

To answer your question, we need to clarify how priority and focus function during a showdown.

According to Rule 313.4, "A player may not make discretionary actions with Focus unless they also possess Priority." Additionally, as clarified in the RiftJudge FAQ (id 7484, 8470), focus and priority are distinct: focus is the "home base" permission to start a chain in an open state, while priority is the right to act on the current chain.

Here is the breakdown of your situation:

The Ruling

You cannot cast En Garde if your opponent is in the process of passing focus to you, because you must have priority to play a card. If your opponent passes priority/focus, you receive it, and you are then the player who can either act or pass back. You cannot "pre-cast" a reaction before you actually hold priority.

However, once focus/priority is passed to you, you can cast En Garde as your action. After that chain item resolves (or if you play it as a reaction to something else), the state will return to Open, and focus will pass back to your opponent. The showdown only ends when both players pass priority/focus consecutively (Rule 348).

Step-by-Step Sequence (The "Immediate Resolution" attempt)

If you are trying to force the showdown to resolve immediately:

1. Opponent has focus and priority: They pass.
2. You receive focus and priority: You now have the right to play. If you play En Garde now, you have opened a Closed State.
3. Closed State: You now hold priority on the chain you just started. If you pass priority to your opponent, they have the opportunity to respond.
4. Opponent passes: If they pass, the chain (your En Garde) resolves.
5. Return to Open State: Once the chain is empty and the state returns to Open, focus automatically passes to your opponent (unless it was an initial chain).
6. Opponent's Turn: Your opponent now has focus and can choose to play an action or pass back to you.

Key Takeaways

• You cannot "force" an immediate end: The showdown only ends when both players pass consecutively while the state is Open. Even if you play a card, your opponent will get a chance to act again before the showdown ends, unless they choose to pass when they receive focus.
• Passing is not permanent: According to RiftJudge FAQ 201, passing focus does not lock you out. If you pass, and your opponent plays a card, you will receive focus again after their chain resolves and have another chance to act.
• Timing: You can only play En Garde when you have priority. You cannot play it while waiting for the game to hand you priority.

In summary, if you want the showdown to end, you should Pass. If your opponent also passes, the showdown ends immediately (Rule 347.3.a). If you play En Garde, you are intentionally keeping the showdown going by adding an item to the chain.