You and target player exchange control of the creature you each control with the greatest mana value. Then exchange control of artifacts the same way. If two or more permanents a player controls are tied for greatest, their controller chooses one of them.
(16/09/2007)
No permanents are targeted by this effect, so permanents with Shroud may be exchanged this way.
(16/09/2007)
First creatures are exchanged, then artifacts are exchanged. It's possible that the same artifact creature may be involved in both exchanges.
(16/09/2007)
If one of the players doesn't control a creature at the time the exchange would be made, that part of the effect does nothing, but the exchange of artifacts will still happen. Similarly, if one of the players doesn't control an artifact at the time the exchange would be made, that part of the effect does nothing.
