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Whenever a player chooses one or more targets, each player reveals the top card of their library. The player who reveals the card with the highest mana value may change the target or targets. If two or more cards are tied for highest, the target or targets remain unchanged. Changing targets this way doesn't trigger abilities of permanents named Psychic Battle.
The converted mana cost of a split card is determined by the combined mana cost of its two halves.
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.
You can change all, some, or none of the targets.
You can’t change the number of targets, choose an illegal target, or make something get targeted more than once.
