Palladia-Mors, the Ruiner

Commander is where Palladia-Mors, the Ruiner does her best work — six mana is routine in a format built around 40 life and ramp staples, and the hexproof-until-she-attacks clause forces opponents to react at instant speed or eat a trample hit before they can point removal at her. In Legacy and Vintage she's legal but irrelevant; the formats are too fast and efficient for a six-mana creature that doesn't immediately end the game. Modern and Pioneer are similarly unkind — six mana with no enters-the-battlefield effect doesn't compete when the format clock is measured in turns, not value loops. Oathbreaker can support her as a signature spell target or value piece in a Naya shell, but the smaller deck size makes her feel like a finisher rather than an engine.