Cheapest priced copy (The Brothers' War): $0.49 at Card Kingdom, near mint, their price list as of .
Thran Spider 
Artifact Creature — Spider · 2/4 · Rare · The Brothers' War · #368
Reach
When this creature enters, you and target opponent each create a tapped Powerstone token.
{7}: Look at the top four cards of your library. You may reveal an artifact card from among them and put it into your hand. Put the rest on the bottom of your library in a random order.
Legal inCommanderPioneerModernLegacyVintage
Not legal inBrawlStandardPauper
4 printings · $0.49 to $2.49 at Card Kingdom
| Set | Number | Rarity | Card Kingdom | Foil |
|---|---|---|---|---|
| The Brothers' War | 254 | Rare | $0.49 | $0.49 |
| The Brothers' War | 368 | Rare | $0.49 | $0.79 |
| The Brothers' War Promos | 254p | Rare | $0.49 | $2.49 |
| The Brothers' War Promos | 254s | Rare | — | $1.49 |
3 rulings from Wizards of the Coast
- 14 October 2022You can use the {C} added by a Powerstone token on anything that isn't a nonartifact spell. This includes paying costs to activate abilities of both artifact and nonartifact permanents, paying ward costs, and so on.
- 14 October 2022Although all the cards in The Brothers' War that create Powerstone tokens create a tapped Powerstone token, entering the battlefield tapped isn't part of the token's definition. Notably, if you create a token that is a copy of a Powerstone token, the token copy won't enter the battlefield tapped.
- 14 October 2022Powerstone tokens are a kind of predefined token. Each one has the artifact subtype "Powerstone" and the ability "{T}: Add {C}. This mana can't be spent to cast a nonartifact spell."