Veiled Apparition

It enters as an enchantment and waits, doing nothing, until an opponent casts a spell. That trigger is the entire design: it converts the permanent into a 3/3 flyer at the moment the opponent commits to the stack, often after they have already tapped out for the turn. The conversion is permanent, not a flicker; once it has become a creature, it stays one, which means the recurring upkeep tax kicks in immediately. The card cannot dodge removal indefinitely by hiding as a noncreature, because the same spell that earns you the body also locks in the obligation to keep paying for it. That payment is the balancing pressure: a 3/3 with evasion is a real clock, but holding it costs mana every turn or it dies, so the card forces a choice between racing while the flyer is live and treating the tax as rent on a threat that arrived for cheap. The interesting part is the window. Because the trigger keys off an opponent's spell rather than your own action, the body materializes on their turn, frequently as a surprise blocker or as pressure that lands exactly when they thought the board was settled. It is an early experiment in a permanent the opponent cannot fully read on their own clock, an idea later formats would explore at far greater scale, here packaged with an upkeep cost sharp enough to keep the reward modest.