Aven Farseer

The trigger keys off the morph subgame as a whole, not your half of it. Most counter-rewards fire on your own actions: this one cashes in whenever any permanent is turned face up, regardless of who controls it. Flip a face-down creature to ambush an attacker, and the Bird grows. Your opponent unmorphs to surprise you, and the Bird grows anyway. That symmetry is what makes the design unusual: it treats the face-down minigame as a shared resource and skims a counter off every interaction with it. The flying body is the right chassis for that engine, since evasion turns each counter into damage that gets through against ground boards (flyers and reach creatures can still block it). A two-drop that begins as a 1/1 can end a counter-rich game hitting for three or four through the air, having spent nothing but the morph plays both sides were already making. The ceiling is the same thing as the appeal: the payoff lives entirely inside one mechanic, so in an environment with no face-down permanents the trigger never fires and the card sits as a small flier with text it cannot use. Where the morph game is live, it quietly taxes any opponent who chooses to play it, which is the most interesting thing a one-mechanic payoff can do: make the central interaction asymmetrically yours without ever asking you to control the permanents that feed it.