Quickchange

In Commander, Quickchange earns its slot in tribal decks that can exploit creature-type switching — changeling synergies, lords, or sacrifice engines that care about a specific type — and in blue decks that want cheap instant-speed protection against targeted removal. In Pauper it's a fringe combat trick with real applications in tempo shells. Legacy and Vintage have no interest; those formats play at a speed where a one-mana cantrip-level effect needs to do more work than Quickchange offers. Oathbreaker mirrors Commander's logic: if your planeswalker's signature spell can loop Quickchange meaningfully, it overperforms; otherwise it stays on the bench.