Enchantment, 3RR (5) Whenever an artifact, creature, or enchantment enters the battlefield, its controller chooses target permanent another player controls that shares a card type with it. Exchange control of those permanents.1
Illus. Ron Spencer
10/4/2004: The exchange isn't optional. If there is a legal choice, you must make one.
12/1/2004: The permanents have to share a permanent type both when the target is chosen and when the ability resolves.
12/1/2004: Even though Confusion in the Ranks triggers only when an artifact, creature, or enchantment enters the battlefield, the ability can target a land if the permanent entering the battlefield is an artifact land.
12/1/2004: The permanents are exchanged only if they're both on the battlefield when the ability resolves.
12/1/2004: Confusion in the Ranks triggers on itself entering the battlefield. If an opponent controls an enchantment, exchange Confusion in the Ranks for that enchantment.
Mirrodin
(Rare)