Dual Nature

Commander is where Dual Nature actually lives — the format's high-power creatures and enter-the-battlefield value engines make a symmetrical doubling enchantment genuinely threatening, and six mana is easily reachable by mid-game. The symmetry is the real cost: opponents get the same trigger, so Dual Nature rewards decks that can exploit it faster or protect it better than anyone else at the table. Legacy and Vintage technically allow it, but the card is too slow and too parasitic on creature-heavy strategies to compete in those formats. Oathbreaker is the only other format where it sees any real consideration, and only in creature-dense builds that can close quickly.