Cheapest priced copy (Commander 2011): $0.59 at Card Kingdom, near mint, their price list as of .
Conundrum Sphinx 
Creature — Sphinx · 4/4 · Rare · Commander 2011 · #42
Flying
Whenever this creature attacks, each player chooses a card name. Then each player reveals the top card of their library. If the card a player revealed has the name they chose, that player puts it into their hand. If it doesn't, that player puts it on the bottom of their library.
Legal inCommanderModernLegacyVintage
Not legal inBrawlStandardPioneerPauper
3 printings · $0.59 to $0.99 at Card Kingdom
| Set | Number | Rarity | Card Kingdom | Foil |
|---|---|---|---|---|
| Commander 2018 | 84 | Rare | $0.69 | — |
| Commander 2011 | 42 | Rare | $0.59 | — |
| Magic 2011 | 51 | Rare | $0.69 | $0.99 |
2 rulings from Wizards of the Coast
- 15 August 2010If a card a player reveals this way is the card that particular player named, they must put it into their hand. Otherwise, they must put it on the bottom of their library, even if it’s the card a different player named. In no cases can a player leave the revealed card on top of their library.
- 15 August 2010First the player whose turn it is names a card, then each other player in turn order does the same. Then each player reveals the top card of their library at the same time.