Air Bladder

Granting flying is normally an offensive upgrade: push a body over the top, finish through the air, convert a ground attacker into an evasive clock. This Aura still does all of that. The enchanted creature gains flying with no strings attached to attacking, so for a single blue mana you can hand any ground creature the skies and start swinging unanswered. The catch lives entirely on defense: the creature can block only fliers. That restriction is what keeps a one-mana evasion enabler from being absurd. A creature wearing this can no longer wall the ground; it has traded its ability to stand in front of a charging beast for the ability to threaten and contest the air. The card therefore plays at both ends of the board. Behind, it points a creature upward to trade with an opposing flier you otherwise could not reach. Ahead, it cheaply turns a beater into a threat the ground cannot block, the cost being that the same creature can no longer hold the line below. The lopsidedness is real, but it cuts against blocking grounded creatures, not against attacking. This is the cheap-evasion-Aura school whose entire pitch is rate: a one-mana effect that, in most other costings, would carry a body or a steeper downside, here paying for its discount by surrendering ground defense outright.