Instructions very confusing on this one. Without knowing the mechanic, I would be very confused as to how to play this. It seems to be pick a side, play it, then later turn you can pay to unlock the other side. But why the reminder "that door unlocks"?
I looked up the rules, and holy shit is it confusing when you get into detail.
-
You cast an Enchantment with a Room subtype and pay for either side. You ignore the other side.
-
If the Room has one side unlocked, you may unlock the other by paying the cost of the other side. This doesn't use the stack, and can't be responded to. Triggers that occur because of this can be responded to.
-
If the Room has neither side unlocked (maybe it got put into the battlefield with Open the Vaults or it got blinked), you can only open a side at sorcery speed, regardless of what was said in the bullet point above.
-
The mana value of a Room is equal to the unlocked doors. This room can have a mana value of 0, 2, 6, or 8, depending on what's unlocked.
-
If you copy a Room, you copy what is and isn't unlocked.
Functionally, it's not bad, but the corner cases these cards have is crazy.
-
Probably there are ability triggers like "when a door unlocks". The reminder could be there to make clear that these effects also trigger when a room is cast and that it does not enter already unlocked.
