Cheapest priced copy (The Brothers' War): $0.79 at Card Kingdom, near mint, their price list as of .
The Stone Brain 
Legendary Artifact · Rare · The Brothers' War · #247
{2}, {T}, Exile The Stone Brain: Choose a card name. Search target opponent's graveyard, hand, and library for up to four cards with that name and exile them. That player shuffles, then draws a card for each card exiled from their hand this way. Activate only as a sorcery.
Legal inCommanderPioneerModernLegacyVintage
Not legal inBrawlStandardPauper
4 printings · $0.79 to $2.99 at Card Kingdom
| Set | Number | Rarity | Card Kingdom | Foil |
|---|---|---|---|---|
| The Brothers' War | 247 | Rare | $0.79 | $0.79 |
| The Brothers' War | 367 | Rare | $1.29Out of stock | $1.49 |
| The Brothers' War Promos | 247p | Rare | $0.99 | $0.79 |
| The Brothers' War Promos | 247s | Rare | — | $2.99 |
5 rulings from Wizards of the Coast
- 14 October 2022You don't have to exile each card you find with that name. If you want to leave one in their graveyard, for example, you may.
- 14 October 2022Unlike most effects of this kind, The Stone Brain's ability allows its controller to choose the name of a basic land. Note that you may only search for up to four copies of that card, even if you find more of them.
- 14 October 2022You don't have to choose the name of a card that you've already seen this game; you may guess at a card you think your opponent might have in their deck, if you'd like.
- 14 October 2022The ability has no effect on permanents with the chosen name that are on the battlefield.
- 14 October 2022You target a player as The Stone Brain's activated ability is put on the stack, but you don't name a card until it resolves. Notably, this means that players don't get to respond to the ability knowing what card you will name.