Heartmender

Heartmender is a Commander card through and through — the payoff is cumulative, and three other players' worth of -1/-1 counter effects give it plenty to clean up over a long game. In Legacy and Vintage it's legal but irrelevant; the formats move too fast for a four-mana creature that does nothing the turn it enters. Modern has enough Infect and Hapatra-adjacent shells to make Heartmender theoretically interesting, but it never cracked those lists in practice. Commander is where it earns its slot, specifically in Atraxa, Praetors' Voice builds and any Hapatra, Vizier of Poisons or Yawgmoth, Thran Physician shell that generates -1/-1 counters as a resource.