Dreamtail Heron

Mutate's central promise was that stacking creatures should feel like building something rather than replacing it, and this is the payoff engine that made the mechanic worth the trouble. A 3/4 flyer for five is a fair enough body on its own, but the draw trigger keys off the act of mutating, not off casting the spell or attacking, which means every time you fold it onto an existing pile you refund a card. Because a single creature can absorb multiple mutations over a game, the trigger is repeatable in a way a plain enters-the-battlefield cantrip is not: each new layer dropped onto the stack, from this or from any other mutate spell landing on the same target, fires the draw again. That reframes the archetype from a fragile all-in on one target into a value grind, where the flying evasion carries a growing bundle of stacked abilities and the pile keeps you stocked with fuel. The problem that usually dooms "voltron on one creature" strategies is that the more you invest in a single body, the harder a single removal spell punishes you. By paying you a card for the assembly step itself, this softens that exposure before the pile even gets going, which is why it sat at the quiet center of nearly every deck built to abuse the mechanic.