Room

Room is a enchantment subtype introduced in Duskmourn: House of Horror to represent the twisted, labyrinthine nature of the plane.
==Description==
Rooms are similar to split cards, a Magic card with two card faces on the front side and a standard Magic card back, but with a major fundamental difference: they're permanent cards. Each side of a Room is called a door. As with all split cards, players can cast only one half from their hand. Pick one half to cast, and that door unlocks on the battlefield, giving you access to that half's abilities. 
The other half of a room can be unlocked when it is on the battlefield, by paying the locked half's mana cost any time you could cast a sorcery. Unlocking a door this way is a special action (it doesn't use the stack and can't be responded to). Unlocking the second half of a Room doesn't affect the half that's already unlocked. It stays unlocked and all abilities on both halves of the card are active and/or usable.
While on the battlefield, a Room card only has the characteristics of its unlocked doors. If one door is unlocked, it will only have the characteristics of that half of the card. If both doors are unlocked, it will have the combined characteristics of both halves. This includes the permanent having two names.
If a Room card enters the battlefield without being cast, both doors will start locked. The permanent will be an object on the battlefield but with no name or abilities and a mana value of zero. It's still a Room enchantment. You can still unlock any locked door by paying that half's mana cost as a sorcery.
===Design background===
Locations are often lands, but lands have a lot of mechanical restrictions. Enchantments are the next best choice as a lot of the essence of a location (especially in Duskmourn) is the feel of the place.
Rooms have the feel of Adventure or Aftermath cards, where one side is cast after the other; however, Rooms can have either side first. Some Rooms have no effect once both sides are unlocked, as both are triggers when unlocked, making them akin to double-Sorceries.
==Rules==
==Rulings==
*To cast a Room spell, choose a half (or "door") to cast. There's no way to cast both halves of a Room card. When the Room spell resolves, the corresponding door becomes unlocked as the Room enters.
*Room cards have two card faces with a shared type line on a single card. The characteristics of the door you didn't cast are ignored while the spell is on the stack.
*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.
*Each Room card has two names. If an effect instructs you to choose a card name, you may choose one of those names, but not both.
*If an effect allows you to cast a spell with certain characteristics, consider only the characteristics of the door you're casting. For example, if an effect allows you to cast a permanent spell with mana value 3 or less from among cards in your graveyard, you could cast Bottomless Pool this way, but not Locker Room.
*While in any zone other than the stack or the battlefield, a Room card's characteristics are a combination of its two doors. For example, <c>Bottomless Pool // Locker Room</c> has a mana value of 6 while it's in your library. If an effect allows you to search your library for a card with mana value 4 or less, you can't find <c>Bottomless Pool // Locker Room</c>.
*While on the battlefield, a Room's characteristics are a combination of the characteristics of its unlocked doors. For example, if <c>Bottomless Pool // Locker Room</c> is on the battlefield with both doors unlocked, its names are Bottomless Pool and Locker Room, its mana value is 6, it's a Room Enchantment, and it has the abilities in each door's text box.
*If a spell or ability would create a copy of a Room spell on the stack, the copy retains the choice of which door was cast but also retains the full characteristics of the spell. The characteristics of the door that wasn't cast are still ignored while the copy is on the stack, and when the copy resolves, the token it becomes will enter with the appropriate door unlocked.
*If a Room enters from any zone other than the stack, it will enter with both halves locked.
*If neither door of a Room is unlocked, it's a Room enchantment with no name and no abilities.
*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.
*An ability that triggers "when you unlock this door" triggers when that door becomes unlocked. This can happen one of two ways: (1) the door becomes unlocked on the battlefield or (2) the door becomes unlocked as the Room enters the battlefield because you cast the corresponding half. In the latter case, since the door becoming unlocked is what causes the ability to trigger, effects that cause abilities that trigger when a permanent enters to trigger an additional time (such as that of <c>Panharmonicon</c>) won't apply.
*Some abilities allow you to unlock a door of a Room you control. You can't choose to unlock a door that's already unlocked with such an ability. If such an ability requires a target, you can target a Room even if both of its doors are unlocked, but the ability won't do anything when it resolves.
*Some abilities allow you to lock a door of a Room you control. You can't choose to lock a door that's already locked with such an ability. If such an ability requires a target, you can target a Room even if both of its doors are locked, but the ability won't do anything when it resolves.
*Some doors have abilities that trigger whenever you unlock that door and require one or more targets. You can unlock that door even if there would be insufficient legal targets for that triggered ability. The triggered ability won't go on the stack.
*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.
==Example==
==References==