An ability that triggers "whenever you fully unlock a Room" triggers when a door becomes unlocked and the other door of that Room is already unlocked, or when both doors of that Room become unlocked simultaneously.
Surgical Suite // Hospital Room
Any time you have priority during a main phase of your turn and the stack is empty, you may pay the mana cost of a locked door (also called its "unlock cost"). That door becomes unlocked. This is a special action. It doesn't use the stack and can't be responded to.
Each Room card is a single card. For example, if you discard a Room card, you've discarded one card, not two. If an effect counts the number of enchantment cards in your graveyard, Bottomless Pool // Locker Room counts once, not twice.
Magic: The Gathering · ™ & © Wizards of the Coast · Illus. Titus Lunter
Card data via Scryfall. Rarix is fan-made; not endorsed by the rights holders.
