Gideon, Champion of Justice

In Commander, Gideon, Champion of Justice scales with the number of opponents — in a four-player pod he can accumulate loyalty absurdly fast, and his indestructible creature mode turns that pile of counters into a genuine threat. The problem is the one-turn delay: every opponent gets a full turn to answer him before he attacks, and at four mana he's competing with planeswalkers that provide immediate value. In Modern and Pioneer he's simply outclassed — four mana for a planeswalker that doesn't affect the board on resolution is a liability in those formats. Legacy and Vintage move too fast for him to matter. Oathbreaker is his best home outside Commander, where he can serve as the actual oathbreaker in a white go-wide shell and his passive loyalty gain becomes a reliable clock.