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Return target permanent to its owner's hand. Return target permanent card from your graveyard to your hand.
If only one target is still legal as Aether Helix tries to resolve, it will still resolve and perform the appropriate action on the remaining target.
You must choose two legal targets in order to cast Aether Helix. If there are either no permanent cards in your graveyard or no permanents on the battlefield, you cannot begin to cast it.
