Appa, Loyal Sky Bison

Appa, Loyal Sky Bison is legal across every major constructed format but belongs almost exclusively in Commander, where a repeatable land-per-attack trigger compounds across a long game. In Standard, Pioneer, or Modern, a five-mana 4/4 that requires attacking to generate value is too slow and too easily answered before the engine starts — there's no competitive build that wants this over faster threats. Commander is the format where Appa earns its slot: 40-life games give it time to attack twice or three times before an opponent can profitably answer it, and multiplayer math means at least one player is often tapped out on your turn. Oathbreaker shares enough of the long-game structure to make Appa playable there too, particularly in green-based ramp shells that can protect it.