Falconer Adept

The design trick here is that the Bird arrives already committed to combat: tapped and attacking, on the same swing that made it. That timing is the whole value proposition. A body that just made flyers at end of turn would be a slow token engine; one that makes them mid-attack turns every combat into an immediate two-body clock, one on the ground and one in the air, with the flier bypassing anything that could only block the base creature. It also means the tokens dodge summoning sickness by never needing to tap on their own initiative, and they contribute to any "attackers you control" or go-wide payoff the moment they enter. The cost of that tempo is that the Birds live and die on the attack step: they show up with the swing, and if the ground creature is held back or removed, the engine simply stops producing. That is the restriction that keeps a repeatable flying-token maker off the top of the curve. It sits in the long line of white creatures that reward attacking by widening the board as they do it, but the attacking-token clause makes it more aggressive than a passive generator: this is a card that wants to be swinging, not sitting behind a wall building an army for later.