Cheapest priced copy (Zendikar): $0.69 at Card Kingdom, near mint, their price list as of .
Cosi's Trickster 
Creature — Merfolk Wizard · 1/1 · Rare · Zendikar · #45
Whenever an opponent shuffles their library, you may put a +1/+1 counter on this creature.
Legal inCommanderModernLegacyVintage
Not legal inBrawlStandardPioneerPauper
1 printing · $0.69 to $1.99 at Card Kingdom
| Set | Number | Rarity | Card Kingdom | Foil |
|---|---|---|---|---|
| Zendikar | 45 | Rare | $0.69 | $1.99 |
3 rulings from Wizards of the Coast
- 1 October 2009The 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.”
- 1 October 2009If 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.
- 1 October 2009Cosi’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.