mtg put card from hand on top of library Rules Text: creature card, your graveyard your library., 12 cards Search the City | Return

Like most Magic: The Gathering cards, the value of Geralf's Masterpiece depends on a few consistent factors: its rarity, the printing and finish (regular or foil), its physical condition, and the set it was printed in (Shadows over Innistrad)

It uses the stack, but it is not casting a spell

If the creature it's enchanting leaves the battlefield for any reason, the Aura immediately becomes an enchantment creature again rather than being put in the graveyard like other Auras

Note that this does not read, nontoken creature so you can just abuse a token making deck where most or all of the creatures are of the same type, like Drakes for a Talrand, Sky Summoner deck, as one example