Cheapest priced copy (Foundations): $0.35 at Card Kingdom, near mint, their price list as of .
Brineborn Cutthroat 
Creature — Merfolk Pirate · 2/1 · Uncommon · Foundations · #152
Flash (You may cast this spell any time you could cast an instant.)
Whenever you cast a spell during an opponent's turn, put a +1/+1 counter on this creature.
Legal inCommanderBrawlStandardPioneerModernLegacyVintage
Not legal inPauper
5 printings · $0.35 to $0.49 at Card Kingdom
| Set | Number | Rarity | Card Kingdom | Foil |
|---|---|---|---|---|
| Foundations | 152 | Uncommon | $0.35 | $0.49 |
| Game Night: Free-for-All | 24 | Uncommon | $0.39 | — |
| Jumpstart 2022 | 278 | Uncommon | $0.35 | — |
| Foundations Jumpstart | 291 | Uncommon | $0.35 | — |
| Core Set 2020 | 50 | Uncommon | $0.35 | $0.49 |
2 rulings from Wizards of the Coast
- 12 July 2019Brineborn Cutthroat's ability resolves before the spell that caused it to trigger. It resolves even if that spell is countered.
- 12 July 2019Brineborn Cutthroat must be on the battlefield for its last ability to function. Notably, the ability won't trigger as you cast Brineborn Cutthroat during an opponent's turn.