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Whenever an opponent shuffles their library, you may put a +1/+1 counter on Cosi's Trickster.
Cosi’s Trickster’s ability triggers when an opponent shuffles their library because that player was instructed to do so by a spell or ability that specifically contains the word “shuffle” in its text or (in the case of a keyword ability) in its rules.
If an opponent’s library is empty or has just a single card in it when a spell or ability instructs that player to shuffle their library, Cosi’s Trickster’s ability will still trigger.
The cascade ability doesn’t cause a player to shuffle their library, even if that player revealed their entire library. The revealed cards are put on the bottom of their owner’s library in a random order, but they’re not “shuffled.”
