cr:9.1.4a

If a twin-card is outside the arena and not on the stack, both of its faces are active.

Example: Levia, Redeemed // Blasmophet, Levia Consumed is a twin-card with the text “Action – Turn all cards in your banished zone face-down: Transform into Levia, Redeemed. Activate this ability only while this is in your inventory and you have 13 or more cards with blood debt in your banished zone.” and “While this is in your inventory, when blood debt reduces your {h} to 13, you may transform into Blasmophet, Levia Consumed.” respectively. While this card is in a player’s inventory, both of these abilities are functional because the card as a whole has both sets of properties from both its faces.