Roc Egg

A wall that improves when it dies. The 0/3 body with Defender is built to absorb the early aggressive turns; the death trigger means trading it away or sacrificing it converts a stationary blocker into a 3/3 flier that swings the air for you. That reversal is the whole design: opponents pay a real cost to break through, because killing the Egg hands you the better creature, and the body that was holding the ground becomes the one taking the skies. It rewards the controller's patience without punishing the trade, a clean two-stage payoff packaged at a low rarity. The lineage runs through the various "hatch into something bigger" eggs and the broader white tradition of defensive creatures that earn their keep on death rather than in combat. The friction worth noting is timing: the flier only arrives once the Egg is gone, so it asks you to either let the blocker die naturally or feed it to a sacrifice effect, never to have both the wall and the bird at once.