Esperzoa

A 4/3 flyer for three mana is a genuinely aggressive rate in blue, and the mandatory upkeep bounce is what the body is paying for it. But the design is built to be exploited rather than tolerated: the trigger says return an artifact you control, so a single cheap enters-the-battlefield artifact reloads on demand every turn. The artifacts worth feeding it are the ones whose value is front-loaded into an ETB and stays on the battlefield: a manifold mana rock, a creature whose enter trigger you want again, anything that pays you for re-entering the battlefield rather than for sacrificing itself. That last distinction is where the loop earns its limits. One-shot artifacts that immolate themselves as a cost are exactly the wrong partners; they are already gone before the upkeep trigger resolves, with nothing left to return. So the engine wants permanents that linger and reward replay, fed by a clock that closes games while you assemble them. The constraint that keeps it honest is the word "an": if it is the only artifact you control, it bounces itself, leaving you with no flyer and a card back in hand. So it asks for a board that always holds a cheaper artifact to feed it, which is the kind of artifact-dense shell where its body matters least and its trigger most. It belongs to the small lineage of creatures whose downside reads as the draft of a combo loop waiting for the right partner.