Cheapest priced copy (Adventures in the Forgotten Realms): $0.35 at Card Kingdom, near mint, their price list as of .
Thieves' Tools 
Artifact — Equipment · Common · Foundations Jumpstart · #126
When this Equipment enters, create a Treasure token. (It's an artifact with "{T}, Sacrifice this token: Add one mana of any color.")
Equipped creature can't be blocked as long as its power is 3 or less.
Equip {2} ({2}: Attach to target creature you control. Equip only as a sorcery.)
Legal inCommanderPioneerModernLegacyVintagePauper
Not legal inBrawlStandard
3 printings · $0.35 to $0.49 at Card Kingdom
| Set | Number | Rarity | Card Kingdom | Foil |
|---|---|---|---|---|
| Adventures in the Forgotten Realms | 122 | Common | $0.35 | $0.49 |
| Commander Legends: Battle for Baldur's Gate | 152 | Common | $0.35 | $0.49 |
| Foundations Jumpstart | 126 | Common | $0.35 | — |
One ruling from Wizards of the Coast
- 23 July 2021The equipped creature's power is checked only during the declare blockers step. If its power becomes greater than 3 after blockers are declared, it still can't be blocked. Similarly, if its power becomes 3 or less after it's been blocked, this won't make it unblocked.