Metathran Aerostat

The activation pays the creature's mana value plus one blue, so this is not a cost-cheat in the polymorph or reanimation sense: an X equal to the bigger creature's mana value means you spend one mana more than just casting it outright. What the extra mana buys is delivery, not discount. The creature enters the battlefield rather than the stack, dodging counterspells, and the self-bounce hands the Aerostat back to you so the same flier can deploy again next turn. That recursion is the design's actual hook, the thing that turns a single enabler into a reusable engine. The bounce is also the price: each use strips a 2/2 flier off the board, so the play only profits when the creature arriving outweighs the body you just surrendered. Because it is an ordinary activated ability, the deployment defaults to instant speed, and that is where the engine earns its keep: you can hold the mana up as a bluff, slip a fattie into play during an opponent's end step, or wait until both the creature and the spare mana line up. The lineage here is blue's permanents-into-play tradition, sharing a family resemblance with Elvish Piper, where the creature itself becomes the deployment platform rather than a card you cast. The distinguishing wrinkle is that the platform survives its own use, returning to hand intact instead of staying tapped on the table waiting to die.