Cheapest priced copy (Duel Decks: Merfolk vs. Goblins): $0.35 at Card Kingdom, near mint, their price list as of .
Triton Tactics 
Instant · Uncommon · Duel Decks: Merfolk vs. Goblins · #23
Up to two target creatures each get +0/+3 until end of turn. Untap those creatures. At this turn's next end of combat, tap each creature that was blocked by one of those creatures this turn and it doesn't untap during its controller's next untap step.
Legal inCommanderPioneerModernLegacyVintage
Not legal inBrawlStandardPauper
3 printings · $0.35 to $0.49 at Card Kingdom
| Set | Number | Rarity | Card Kingdom | Foil |
|---|---|---|---|---|
| Duel Decks: Merfolk vs. Goblins | 23 | Uncommon | $0.35 | — |
| The List | DDT-23 | Uncommon | $0.35 | — |
| Theros | 71 | Uncommon | $0.35 | $0.49 |