Heroes' Bane

The activated ability is the entire trick: most counter-doublers and growth engines ask you to invest mana for a fixed return, but this one scales with what it has already become. The cost stays flat while the payoff compounds, because X is the creature's current power. Start at the four counters it brings along, pump once to eight, again to sixteen, then thirty-two: each activation roughly doubles the body, and the mana stays constant. That is exponential growth gated only by how many times you can untap and pay four. The discipline that keeps it from being broken is the body it starts as: a 0/0 base that lives entirely on its counters, vulnerable to any wrath, any -X/-X, any edict before it gets going, and useless on the turn it lands without mana to spare. It is a green Hydra built to do one thing, the thing green Hydras have always promised: get arbitrarily large if left alone. The squeeze is the activation cost relative to the clock; four mana per doubling means the early activations are slow and the late ones win on the spot, so the question is always whether the opponent can interact before the geometric curve outruns them.