Avenger of the Fallen

Avenger of the Fallen is legal across every major format but its design speaks almost exclusively to Commander, where legendary creatures are the rule rather than the exception and a steady death trigger becomes a repeatable engine. In 60-card formats like Modern and Pioneer, legendary density is too inconsistent to build around, and a five-mana 3/3 with a conditional trigger simply doesn't compete with what those formats demand at that cost. Standard gives it the most generous environment outside of Commander, but even there the payoff is too slow and conditional without a dedicated legendary shell to support it. Commander is where Avenger of the Fallen actually does what it promises — legendary creatures die constantly, whether to combat, removal, or sacrifice outlets, and a free 2/2 each time compounds fast enough to matter.