Serrated Biskelion

A self-destructing pinger, and the symmetry is exactly what keeps it honest. Every activation costs the Biskelion a point of toughness alongside the target, so the clock runs both ways: as a 2/2, it can fire twice before the second -1/-1 counter drops its own toughness to zero and a state-based action kills it. Those two taps shave two toughness off something else, then the engine is gone for good. That is the calibration: a body that can answer a small creature outright or chip a larger one down, but only at the price of grinding itself out of existence in two installments. The design discipline is the permanent counter. The -1/-1 markers stay on the body with no way to reset them between turns, so the card you start a game with is strictly better than the one you finish with, and the number of activations is fixed before you ever untap. That permanence separates it from a regenerating duelist or a firebreathing attacker: this is a one-way grind, a construct designed to trade itself away in measured pieces rather than recover. The artifact frame is what made it useful, repeatable creature removal that asked for no color commitment in an era when most repeatable answers demanded one, and the tap cost keeps it from acting the turn it lands or while it is summoning-sick. A blunt instrument, but a precisely metered one: every point it deals is a point it spends.