Cheapest priced copy (Mystery Booster 2): $0.49 at Card Kingdom, near mint, their price list as of .
Goblin Guide 
Creature — Goblin Scout · 2/2 · Rare · Secret Lair Promo · #23
Haste
Whenever this creature attacks, defending player reveals the top card of their library. If it's a land card, that player puts it into their hand.
Legal inCommanderModernLegacyVintage
Not legal inBrawlStandardPioneerPauper
8 printings · $0.49 to $9.99 at Card Kingdom
| Set | Number | Rarity | Card Kingdom | Foil |
|---|---|---|---|---|
| Double Masters | 127 | Rare | $0.79 | $1.99 |
| Double Masters | 347 | Rare | $3.49 | $1.99 |
| Mystery Booster 2 | 58 | Rare | $0.49 | — |
| Modern Masters 2017 | 96 | Rare | $0.79 | $1.49 |
| Grand Prix Promos | 2012a | Rare | — | $6.49 |
| Love Your LGS 2021 | 4 | Rare | — | $0.69 |
| Secret Lair Promo | 23 | Rare | $1.79Out of stock | $9.99 |
| Zendikar | 126 | Rare | $1.99 | $4.99Out of stock |
2 rulings from Wizards of the Coast
- 7 August 2020If Goblin Guide is attacking a planeswalker, that planeswalker's controller is the defending player.
- 7 August 2020If the defending player reveals a nonland card, it remains on top of their library.