Hazoret's Undying Fury

Hazoret's Undying Fury is a Commander card through and through — the free-cast effect scales with the high average CMC most EDH decks run, and the anti-sequencing restriction on casting spells afterward is nearly irrelevant when you've already generated four permanents for six mana. In competitive 60-card formats like Legacy, Modern, and Pioneer, the sorcery speed and the inability to chain cantrips off the hits make it too clunky to see real play; those formats want consistent, low-to-the-ground lines, not a six-mana gamble. Vintage has the raw power density to ignore most cards at six mana. Oathbreaker is a reasonable home for the same reasons Commander is — the curve is often high enough to generate value — but the smaller deck size slightly increases variance on hitting live spells.