Grizzled Wolverine

Three locks stack onto the pump, and reading them in order shows the whole design: it fires only during the declare blockers step, only when at least one creature is already blocking, and only once each turn. The sequence is the point. By the time the +2/+0 is available, the defender has committed and the blocks are locked; there is no taking them back. The 2/2 body invites a trade against a comparable blocker, which is the bait, and a single red mana swings the math to 4/2: enough to deal lethal to most things that stepped in front of it. What it does not buy is survival. With no first strike and no toughness boost, the Wolverine still eats whatever damage the blocker assigns and dies alongside it; the trick wins the exchange of bodies, not the creature itself. The once-per-turn cap fixes the worst case at exactly one surprise swing, never a chain climbing out of range, so the attacking player is selling a clean double kill rather than an escape. This is a tightly fenced combat creature whose entire value lives in the decision the opponent makes during a single step of a single combat: block it, and you likely lose the blocker, but you take it down with you.