Hidden Dragonslayer

Megamorph's whole pitch was turning the flip cost into a payoff rather than a tax, and few cards used that better than this one. Cast it face down as a nondescript 2/2 for three, and the disguise itself becomes the threat: at any time you can pay the megamorph cost, turn it face up, and destroy a creature with power 4 or greater an opponent controls. Because the kill fires off being turned face up rather than off a spell resolving, it dodges counterspells entirely, though the destroy itself is a triggered ability that goes on the stack, so a well-timed Stifle or an indestructible-granting effect can still answer it. The catch is the morph commitment. Hard-casting for two gives you a lifelinking 2/1 and nothing else, since the card enters face up and the kill trigger never gets a chance to fire. The removal lives entirely in the face-down line, which means the contingent answer costs you a card invested face down a turn early and three mana up front, then the megamorph cost later to cash it in. The power-4-or-greater clause keeps it from being universal removal bolted to a creature: it answers fatties, dragons, and pumped-up attackers, not the small early threats that out-tempo white anyway. Lifelink finishes the package, turning the 3/2 it becomes into a stabilizer against exactly the oversized creatures the trigger is built to remove.