变形兽精华 (Shapeshifter's Marrow) (zhs)
Enchantment
(CMC 4)
At the beginning of each opponent's upkeep, that player reveals the top card of their library. If it's a creature card, the player puts the card into their graveyard and Shapeshifter's Marrow becomes a copy of that card. (If it does, it loses this ability.)