Does that mean playing an ambush unit is not playing a "spell" and not "activating an ability", and means automatically just passing? And if that's true, when the opponent has passed before, it would start combat?

Question

Accepted Answer

To answer your question, we must look at how playing a unit (such as an Ambush unit) interacts with the rules of a Showdown.

### 1. Playing a Unit is a "Legally Timed" Action
Rule 348 refers to "playing a spell" or "activating an ability," but this is a shorthand for all legal actions a player can take during a Showdown. Rule 347 clarifies what a player with Focus may do:

*   **Rule 347.1:** A player with Focus may **"Play a card that is legally timed."** 
*   **Rule 347.1.a:** **"The card will start a Chain as normal."**

When you play a unit with **Ambush** during a Showdown, you are playing a card that is legally timed (thanks to the Ambush keyword's granted [Reaction] timing). By doing so, you are exercising one of the permitted actions under Rule 347.

### 2. Does Playing an Ambush Unit End the Showdown?
No. Playing a card (including an Ambush unit) is not "passing Focus."

According to Rule 348 and Rule 347.3.a, the Showdown only ends if **all players pass Focus in sequence** without any actions being taken. If you play an Ambush unit, you have taken an action, which resets the sequence of passes.

### 3. Summary of the Flow
*   **If you play an Ambush unit:** You have used your Focus to start a chain. Because you took an action, the "all players have passed" condition for ending the Showdown is **not met**.
*   **The Showdown continues:** After your unit enters play (and any triggered abilities resolve), the state returns to Open. Focus then passes to your opponent, who gets the opportunity to play their own cards or pass. 
*   **Combat Progression:** Combat only proceeds to the damage step if **both players pass Focus consecutively** without playing any cards or activating abilities (Rule 348.1). Playing an Ambush unit prevents this from happening until your opponent subsequently passes their own Focus as well.

In short: **Playing a unit is a distinct action in a Showdown.** It prevents the Showdown from ending and keeps the combat state active, meaning you are not forced into the combat damage step by simply playing a unit.