Cheapest priced copy (Hour of Devastation): $0.35 at Card Kingdom, near mint, their price list as of .
Dauntless Aven 
Creature — Bird Warrior · 2/1 · Common · Hour of Devastation · #7
Flying
Whenever this creature attacks, untap target creature you control.
Legal inCommanderPioneerModernLegacyVintagePauper
Not legal inBrawlStandard
1 printing · $0.35 to $0.49 at Card Kingdom
| Set | Number | Rarity | Card Kingdom | Foil |
|---|---|---|---|---|
| Hour of Devastation | 7 | Common | $0.35 | $0.49 |
2 rulings from Wizards of the Coast
- 14 July 2017All attackers are chosen at once. You can’t attack with Dauntless Aven, untap a tapped creature, and then attack with that creature.
- 14 July 2017Untapping an attacking creature doesn’t remove it from combat.