Is Darius trifarian's a trigger effect or a mandatory effect?

Question

Accepted Answer

Darius, Trifarian's ability is a **triggered ability**, and it is **mandatory** to place on the chain if the condition is met.

According to the core rules and the specific mechanics of Darius, Trifarian:

*   **Triggered Ability:** Darius's ability is a triggered ability because it uses the "When..." structure ("When you play your second card in a turn...").
*   **Mandatory:** Unlike triggered abilities that include the word "may" (which are optional), Darius's ability does not contain "may." Therefore, when the condition is met (the second card of the turn is played), the ability must be placed on the chain.

**Important Nuances:**
*   **"Played" means resolved:** A card is considered "played" once it has fully resolved on the chain.
*   **Darius counts himself:** If you play Darius as your second card of the turn, he sees himself as the second card, and his ability will trigger.
*   **Once per turn:** This ability only triggers once per turn, specifically when the second card is played. It does not trigger for the third, fourth, or subsequent cards.
*   **Accountability:** As the controller of Darius, you are the "accountable player" responsible for acknowledging this trigger. If you fail to acknowledge it before a new game action is taken, it is considered "forgotten" and will not resolve (Rule 506.3).