Cheapest priced copy (Commander Masters): $0.35 at Card Kingdom, near mint, their price list as of .
Brass Knuckles 
Artifact — Equipment · Common · Commander Masters · #372
When you cast this spell, copy it. (The copy becomes a token.)
Equipped creature has double strike as long as two or more Equipment are attached to it.
Equip {1} ({1}: Attach to target creature you control. Equip only as a sorcery.)
Legal inCommanderPioneerModernLegacyVintagePauper
Not legal inBrawlStandard
4 printings · $0.35 to $3.99 at Card Kingdom
| Set | Number | Rarity | Card Kingdom | Foil |
|---|---|---|---|---|
| Commander Masters | 372 | Common | $0.35 | $0.49 |
| Fallout | 227 | Uncommon | $0.35 | $0.99 |
| Fallout | 755 | Uncommon | — | $3.99 |
| Streets of New Capenna | 234 | Uncommon | $0.35 | $0.49 |
2 rulings from Wizards of the Coast
- 29 April 2022A copy of a permanent spell enters the battlefield as a token. This is not the same as an effect that creates a token, and any effect that refers to creating a token does not apply to copies of permanent spells.
- 29 April 2022Multiple instances of double strike do not increase the number of strikes. That creature still only gets to deal combat damage twice.