Cheapest priced copy (Foundations): $0.35 at Card Kingdom, near mint, their price list as of .
Armasaur Guide 
Creature — Dinosaur · 4/4 · Common · Foundations · #3
Vigilance (Attacking doesn't cause this creature to tap.)
Whenever you attack with three or more creatures, put a +1/+1 counter on target creature you control.
Legal inCommanderBrawlStandardPioneerModernLegacyVintagePauper
1 printing · $0.35 to $0.49 at Card Kingdom
| Set | Number | Rarity | Card Kingdom | Foil |
|---|---|---|---|---|
| Foundations | 3 | Common | $0.35 | $0.49 |
One ruling from Wizards of the Coast
- 8 November 2024It doesn't matter what happens to the creatures you attacked with once Armasaur Guide's last ability has triggered. When that ability resolves, you'll put a +1/+1 counter on the target creature regardless of whether the creatures you attacked with (or Armasaur Guide) are still on the battlefield.