Hidden

Hidden is a keyword that acts as a prerequisite to perform the Hide Discretionary Action.

It is present on Spells, Units, and Gear.

It is functionally short for "While this card is in your hand or in your Champion Zone on your turn during an Open State, you may pay [A] to hide this facedown at a battlefield you control that doesn't already have a facedown card hidden there, for as long as you control that battlefield. Beginning on the next turn, this gains [Reaction] and you may play this, ignoring its base cost."

Hide is not a subset of Play; hiding a card is its own Discretionary Action.

Hiding a card does not open a chain, but playing a card from facedown does open a chain.

If a hidden spell or a play effect of a hidden permanent chooses targets, those targets must be chosen from among options at that battlefield, unless the ability explicitly restricts targeting in a way that makes this impossible.

Each target is treated separately and individually when applying the hidden targeting restriction.

A card with Hidden may still be played for its cost as normal, at its normal timing with no restrictions on targeting.

Multiple instances of Hidden are redundant.

A card that is Hidden gains Reaction while facedown or played from facedown. The property is granted to the card in its facedown state and is not publicly known.

Hidden, and whether or not a card has Hidden, is a characteristic of the card and may be checked or referenced by other Game Effects, independent of the state of being facedown.