What it does
Aura Swap is an activated ability found on certain Auras (like those from the Future Sight set). Its cost lets you exchange that Aura on the battlefield with an Aura card in your hand. Essentially, you pay the cost, return the battlefield Aura to your hand, and put the hand Aura onto the same permanent it was enchanting—without paying its mana cost or casting it.
The big nuance people miss: the swapped-in Aura must legally enchant whatever the original was attached to. If the new Aura can't legally attach (wrong enchant type, illegal target), the swap simply doesn't happen and the cost isn't paid. Also, this isn't casting, so it dodges counterspells and ignores the new Aura's normal costs.
In Commander it's a niche, rarely-seen mechanic, but it can recur powerful Auras or dodge sorcery-speed restrictions, swapping in big enchantments at instant speed.
Iconic cards with Aura Swap
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