Vexing Devil

The most honest one-drop ever printed, and the design hinges on handing the decision to the wrong person. A 4/3 for a single red mana is a body with no business existing this early; the wrinkle is that the opponent, not the caster, chooses which half of the card resolves. Cast it on turn one against a control deck happy to absorb four to the face, and you have spent a card and a mana to deal damage a burn spell would have managed cleaner, with no board left behind. Cast it against an aggressive mirror, or into a life total they cannot afford to spend, and they decline, leaving you a 4/3 punching well past its cost (though it enters with summoning sickness, so the clock starts a turn slow). That fork is the whole card: every game it resolves as either a chunk of direct damage or a body that has to wait a turn to swing, and the opponent picks whichever hurts least. The deeper problem it stages is the symmetry-breaking tax in aggressive design, where a card pushed far enough on rate has to give something back, and what it surrenders is agency. The reason it never quite became a fixture despite the math is that the opponent calls it with full knowledge of their own life total, board, and plan, so the four damage tends to land precisely when they were never worried about it.