Can a card with Hidden be played for its normal cost from the facedown zone in the same turn it was hidden?

Ruling: No, a card with Hidden cannot be played from the facedown zone in the same turn it was hidden. Cards can only be played from your hand by default, and the Hidden ability only grants permission to play the facedown card beginning on the next turn.

Sequence:

• When you hide a card, it moves from your hand to the facedown zone at a battlefield
• The card gains the ability to be played as a Reaction beginning on the next turn
• Until then, you have no rule allowing you to play cards from the facedown zone

Nuances:

• You can still play the card from your hand for its normal cost before hiding it (instead of hiding it)
• Once hidden, the card is no longer in your hand, so the default permission to play cards from hand no longer applies
• The Hidden mechanic itself is the only thing granting permission to play facedown cards, and that permission only begins next turn