They are enchantments, and they ask you to unlock things. For instance, if youd like to play Dollmakers Shop/Porcelain Gallery (shown above) youd first pick which side of the card youd like to play
Because he is so solid against other decks, its hard to believe that this card will go unplayed, even if only as a sideboard special
He's also a sizable 5/4 for 6 mana, so he's a Commander damage clock
You'll also be able to regularly retrigger enchantress abilities by returning things to the battlefield with finality counters on them
These are cards such as Shelinda, Yevon AcolyteShelinda, Yevon Acolyte, Tromell, Seymour's ButlerTromell, Seymour's Butler, or Rosa, Resolute White MageRosa, Resolute White Mage
You can find out which set any card belongs to with the set symbol on the (often) right side of the card