What happens to hidden cards after its controller loses control over the battlefield?

Question

Accepted Answer

According to the official rules and FAQs, when a player loses control of a battlefield that has their hidden card on it, the hidden card is sent to the trash.

This is supported by several RiftJudge FAQs:

*   **FAQ 3662:** "Ruling: When a player loses control of a battlefield that has their hidden card on it, the hidden card goes to the graveyard [trash]."
*   **FAQ 3661:** "If you lose control of that battlefield, hidden cards go to trash."
*   **FAQ 7421:** "Hidden cards are removed from battlefields that do not have a unit controlled by the same player present and are placed in their owner's trash."

**Key Nuances:**
*   **Immediate Loss:** Outside of combat, you lose control of a battlefield immediately when your last unit leaves, and the hidden card is trashed at that time (Rule 184.4.c).
*   **Combat Exception:** During a showdown or combat, you maintain control of the battlefield until the combat fully resolves, even if all your units are removed. You may still use your hidden card as a reaction during this window (FAQ 6143). Once the combat/showdown ends, if you have no units remaining, you lose control and the hidden card is trashed (FAQ 4944).
*   **No Interaction Required:** The opponent does not need to interact with the hidden card for this to occur; the loss of control itself triggers the removal (FAQ 6608).