Once during your turn you may pay N ink to put the top card of your deck facedown under this character. Other cards care about how many cards are under a character.
Official rule 8.4 (Comprehensive Rules 2.2.0). This keyword appears on 32 cards: 31 Character, 1 Location. By ink: 8 Ruby, 7 Sapphire, 5 Amethyst, 4 Amber, 4 Steel, 4 Emerald.