Cheapest priced copy (Mercadian Masques): $0.49 at Card Kingdom, near mint, their price list as of .
Karn's Touch 
Instant · Rare · Mercadian Masques · #86
Target noncreature artifact becomes an artifact creature with power and toughness each equal to its mana value until end of turn. (It retains its abilities.)
Legal inCommanderLegacyVintage
Not legal inBrawlStandardPioneerModernPauper
1 printing · $0.49 to $10.99 at Card Kingdom
| Set | Number | Rarity | Card Kingdom | Foil |
|---|---|---|---|---|
| Mercadian Masques | 86 | Rare | $0.49 | $10.99 |
One ruling from Wizards of the Coast
- 1 August 2008A noncreature permanent that turns into a creature can attack, and its {T} abilities can be activated, only if its controller has continuously controlled that permanent since the beginning of their most recent turn. It doesn’t matter how long the permanent has been a creature.