Enchantment, 3UU (5)
Rare
Whenever a player chooses one or more targets, each player reveals the top card of his or her library. The player who reveals the card with the highest converted mana cost may change the target or targets. If two or more cards are tied for highest cost, the target or targets remain unchanged. Changing targets this way doesn't trigger this ability.
Illus. Ray Lago

10/4/2004: With the Split Cards, use the higher of the two costs on the card to compare with the other card.
10/4/2004: You can change all, some, or none of the targets.
10/4/2004: You can't change the number of targets, choose an illegal target, or make something get targeted more than once.
10/4/2004: An empty library will have no card to reveal, so a player with an empty library has no card to compare. The effect looks for the highest cost card of the cards that actually are revealed.
Legal in Vintage (Type 1)
Legal in Legacy (Type 1.5)
Legal in Classic (MTGO)
Legal in Commander