Hulkling, Young Avenger

The clone-on-a-trigger design usually lives in blue, where copy effects are native and shapeshifters like Vesuvan Doppelganger set the template. Grafting it onto a red four-drop that fires off noncreature spells is the twist: instead of choosing a form once, this rebuilds itself every time you cast a noncreature spell, and reverts at end of turn. That temporary window is the leash on the effect. You are not stealing a body permanently; you are borrowing whichever creature on the battlefield answers the current turn's problem, so long as you keep the spells flowing. The retained clauses do more work than they appear to. Staying a 4/4 with flying and holding onto the copy ability makes each transformation additive rather than a downgrade: clone a lumbering ground fatty and you graft flight and self-replication onto its abilities without shedding them. And because the trigger keys off every noncreature cast, a turn stacked with cheap spells can reshape the creature several times over, each cast a fresh target selection responding to whatever blocks or removal have surfaced since the last one. The demand for a spell-dense shell to feed it is an odd request from a hasteless flyer, and that friction (a copy engine that only turns over when the rest of your hand is noncreature spells) is where the deckbuilding puzzle sits.