Cheapest priced copy (Betrayers of Kamigawa): $0.49 at Card Kingdom, near mint, their price list as of .
Slumbering Tora 
Artifact · Rare · Betrayers of Kamigawa · #161
{2}, Discard a Spirit or Arcane card: This artifact becomes an X/X Cat artifact creature until end of turn, where X is the discarded card's mana value.
Legal inCommanderModernLegacyVintage
Not legal inBrawlStandardPioneerPauper
1 printing · $0.49 to $1.49 at Card Kingdom
| Set | Number | Rarity | Card Kingdom | Foil |
|---|---|---|---|---|
| Betrayers of Kamigawa | 161 | Rare | $0.49 | $1.49 |
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.