Cheapest priced copy (Throne of Eldraine): $0.35 at Card Kingdom, near mint, their price list as of .
Garenbrig Squire 
Creature — Human Soldier · 2/2 · Common · Throne of Eldraine · #158
Whenever you cast a creature spell that has an Adventure, this creature gets +1/+1 until end of turn. (It doesn't need to have gone on the adventure first.)
Legal inCommanderPioneerModernLegacyVintagePauper
Not legal inBrawlStandard
1 printing · $0.35 to $0.49 at Card Kingdom
| Set | Number | Rarity | Card Kingdom | Foil |
|---|---|---|---|---|
| Throne of Eldraine | 158 | Common | $0.35 | $0.49 |
3 rulings from Wizards of the Coast
- 4 October 2019Garenbrig Squire's ability resolves before the spell that caused it to trigger. It resolves even if that spell is countered.
- 4 October 2019An effect may refer to a card, spell, or permanent that "has an Adventure." This refers to a card, spell, or permanent that has an adventurer card's set of alternative characteristics, even if they're not being used and even if that card was never cast as an Adventure.
- 4 October 2019If an effect refers to a card, spell, or permanent that has an Adventure, it won't find an instant or sorcery spell on the stack that's been cast as an Adventure.