Fledgling Osprey

The conditional flying here is the whole design conceit: the body stays grounded until you commit an aura to it, at which point it earns evasion as a byproduct of being enchanted. That turns the cheap creature into a deliberate target for whatever buff you stack on top, since the same enchantment that makes it a 1/1 worth attacking with also gives it the means to connect. The reward is symmetrical with the risk: an enchant-creature deck that wants to pour bonuses onto a single threat gets a flier thrown in, but the moment the aura leaves the battlefield (bounce, destruction, the creature dying and dropping the aura with it), any surviving bird reverts to a grounded one-drop. The keyword is rented, not owned, which is what disciplines the trade: you cannot bluff evasion, and a single piece of enchantment removal answers the aura one-for-one while incidentally clipping the wings. This is the kind of creature whose printed stats are a floor and whose aura supplies both the ceiling and the keyword, making the enchantment the thing that matters and the body the thing that carries it. The bird does not die to that removal trade, but it stops mattering, which on the battlefield is usually the same outcome.