Cheapest priced copy (The List): $2.49 at Card Kingdom, near mint, out of stock, their price list as of .
Polymorph 
Sorcery · Rare · Magic 2010 · #67
Destroy target creature. It can't be regenerated. Its controller reveals cards from the top of their library until they reveal a creature card. The player puts that card onto the battlefield, then shuffles all other cards revealed this way into their library.
Legal inCommanderModernLegacyVintage
Not legal inBrawlStandardPioneerPauper
6 printings · $2.49 to $54.99 at Card Kingdom
| Set | Number | Rarity | Card Kingdom | Foil |
|---|---|---|---|---|
| Classic Sixth Edition | 86 | Rare | $5.49Out of stock | — |
| Ninth Edition | 90 | Rare | $4.49Out of stock | — |
| Ninth Edition | 90★ | Rare | — | $54.99Out of stock |
| Magic 2010 | 67 | Rare | $5.99Out of stock | $13.99Out of stock |
| Mirage | 82 | Rare | $6.99 | — |
| The List | M10-67 | Rare | $2.49Out of stock | — |
5 rulings from Wizards of the Coast
- 4 October 2004If there are no creatures in the player’s library, then the target creature is still destroyed, you see all the cards in that player’s library, and then they shuffle and continue play.
- 1 October 2009A “creature card” is any card with the type creature, even if it has other types such as artifact, enchantment, or land. Older cards of type summon are also creature cards.
- 1 October 2009If the targeted creature is an illegal target by the time Polymorph would resolve, the entire spell doesn’t resolve. Nothing else happens.
- 1 October 2009If there are no creature cards in the player’s library, all the cards in that library are revealed, then the library is shuffled. (The targeted creature remains destroyed.)
- 1 July 2013If the targeted creature has indestructible, it’s still a legal target — it just isn’t destroyed. The rest of Polymorph’s effect happens as normal.