Cosi's Trickster — ruling 1

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.

Cosi's Trickster — ruling 2

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.”

Cosi's Trickster — ruling 3

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.

Cosi's Trickster : règles, fonctionnement et interactions (MTG)

Cosi's Trickster is one of those cards players keep asking about. Here is, in plain words, what its official text says, the rulings published by Wizards of the Coast, and the combos players actually run.

Official card text

Whenever an opponent shuffles their library, you may put a +1/+1 counter on this creature.

How it works : Cosi's Trickster

Original English text — Wizards of the Coast / Scryfall

#1October 1, 2009· Wizards of the Coast
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.
No other card is named in this ruling.
#2October 1, 2009· Wizards of the Coast
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.”
No other card is named in this ruling.
#3October 1, 2009· Wizards of the Coast
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.
No other card is named in this ruling.