Arcanum Wings

Aura Swap is the mechanic this card exists to demonstrate, and the demonstration is almost suspiciously cheap: a two-mana flier-granting Aura that, for an additional outlay, retracts itself off the creature and back into your hand in exchange for a heavier enchantment already waiting there. The structural trick is that it sidesteps the cost of casting a big Aura and the tempo loss of a creature dying with that Aura attached. You stick this for two, then pay the swap to drop a finisher-grade Aura onto a board that has already developed, never exposing the expensive permanent to a kill spell on an empty target. There is a catch worth stating plainly: when Arcanum Wings leaves the battlefield to swap, the flying goes with it, so the creature keeps wings only if the incoming Aura grants them too. What the exchange really buys you is a discount on the second enchantment, not a stacking of effects. The wrinkle worth dwelling on is the timing. Aura Swap never puts the incoming Aura on the stack as a spell, so it dodges counterspells aimed at the enchantment you actually want, though the activated ability itself can still be responded to. The price built into the whole maneuver is that you spend a card and mana to convert a small Aura into a large one, which only earns its keep when the creature underneath is worth dressing up twice. As a window into a design idea that has otherwise been left alone, it remains the lowest-stakes one available.