These will transform after you fulfill some kind of condition on the card, usually either an activated ability (i.e., paying to exile Terra, Magical Adept) or triggered ability (i.e., having six permanents in the yard for Exdeath, Void Warlock at end of turn)
So buckle up and join me on a crash course in Aetherdrifts rules of the road
There is not a single B/G deck I can think of that does not improve by the addition of this enchantment
There's a promo card variant with the Magic logo stamp, for instance, which has understandably remained cheap
During the era of the Weatherlight Saga we have winning cards such as Mirri's Guile or Hanna's Custody or Orim's Thunder
A 4-mana 2/3 flyer that forces your opponent to discard is exactly that, and in the earlier part of the game the fact that this bounces a spell is pretty nice