Cheapest priced copy (Zendikar Rising): $0.35 at Card Kingdom, near mint, their price list as of .
Mind Carver 
Artifact — Equipment · Uncommon · Zendikar Rising · #113
When this Equipment enters, attach it to target creature you control.
Equipped creature gets +1/+0. It gets +3/+1 instead as long as an opponent has eight or more cards in their graveyard.
Equip {2}{B}
Legal inCommanderPioneerModernLegacyVintage
Not legal inBrawlStandardPauper
1 printing · $0.35 to $0.49 at Card Kingdom
| Set | Number | Rarity | Card Kingdom | Foil |
|---|---|---|---|---|
| Zendikar Rising | 113 | Uncommon | $0.35 | $0.49 |
4 rulings from Wizards of the Coast
- 25 September 2020If the target creature becomes an illegal target, the Equipment remains on the battlefield unattached.
- 25 September 2020Attaching an Equipment with its enters-the-battlefield triggered ability isn't the same as using its equip ability. You don't pay mana for the attachment, and if the Equipment enters at a time you couldn't cast a sorcery, you can still attach it to a creature you control.
- 25 September 2020An ability that offers a bonus if an opponent has eight or more cards in their graveyard won't provide additional benefits if more than one opponent has eight or more cards in their graveyard. There are also no additional benefits no matter how many cards are in an opponent's graveyard, as long as there are at least eight.
- 25 September 2020In a multiplayer game, once an opponent leaves the game, they won't be considered for such an effect, no matter how many cards they had in their graveyard before leaving the game.