Confusion in the Ranks
Mirrodin — rare
Enchantment
Confusion in the Ranks rulings:
2004-12-01: The permanents have to share a permanent type both when the target is chosen and when the ability resolves.
2004-12-01: 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.
2004-12-01: The permanents are exchanged only if they’re both on the battlefield when the ability resolves.
2004-12-01: Confusion in the Ranks triggers on itself entering the battlefield. If an opponent controls an enchantment, exchange Confusion in the Ranks for that enchantment.
2004-10-04: The exchange isn’t optional. If there is a legal choice, you must make one.