Grey Knight Paragon

Grey Knight Paragon is legal in Commander, Legacy, Vintage, and Oathbreaker, and that's effectively the full picture — it's not legal in Modern, Pioneer, Standard, or Pauper. In Commander it slots into Human tribal decks where a mass first-strike pump on attack can close out a turn that would otherwise stall; the ceiling is high when you're swinging with eight Humans, the floor is a 2/2 for four that trades down. Legacy and Vintage have zero interest in a four-mana creature with a conditional combat trick when those formats reward density and speed above all else. Oathbreaker is the format most likely to find niche use, specifically under a Human-matters spellshaper or token commander where the enter-the-battlefield trigger doubles as a combat finisher.