Panglacial Wurm

The casting permission weaponizes a moment almost nothing else in the game cares about: the brief stretch when your library is open and you are looking through it. Most cards interact from the hand or the battlefield; this one fires from the deck itself, the zone designers normally treat as sealed and hidden. The condition is exact. The permission reads "while you're searching your library," which means any search will do, including one your opponent forced on you with a Field of Ruin activation or an Assassin's Trophy, so long as you have seven mana untapped while that search is still resolving. The full price is the brake: a 9/5 trampler that does nothing for the deck that merely draws it becomes live only when the search, the open mana, and the timing line up at once. The reward is a creature that can land on an opponent's turn, arriving with no telegraph beyond someone deciding to go digging, even if that someone is the opponent who handed you the search by destroying your land. Few designs pay you for what happens inside the library rather than out in the open, and fewer still reward the act of searching at all, no matter who started it.