How does the Hidden keyword work in Riftbound - what are the costs to hide a card, reveal it, and when can it be revealed?

Ruling: To play a card with Hidden, you pay one power (typically by recycling a rune) instead of the card's normal energy cost. When you reveal the hidden card later, you play it for free.

Sequence:

• Pay one power (by recycling a rune) to play the card hidden at a battlefield you own
• Wait until the next player's turn (you cannot reveal it on the same turn you hid it)
• Starting from the next player's turn, you can reveal it as a reaction to play it for free

Nuances:

• You don't have to play a card with Hidden as hidden - you can just pay its normal energy cost to play it as a regular unit
• Hidden cards gain "reaction" as a keyword when hidden
• You cannot hide a champion from the champion zone (it must be played from hand)
• When a hidden unit is revealed and played, it enters exhausted like any other unit being played