When Brynhir is played from Aurora's effect, does Brynhir's effect work during the opponent's turn?

Ruling: No, Brynhir's effect does not work during the opponent's turn when played from Aurora's effect, because it is still your turn when Aurora plays the card.

Nuances:

• Brynhir does not stop opponents from hiding a card, as hiding is not the same as playing a card
• You can only hide a card during your turn
• If Brynhir were somehow played on your opponent's turn (e.g., via Promising Future), they could still hide a card but would not be able to flip it due to Brynhir's effect
• You cannot play a hidden card the same turn it is placed facedown on the battlefield