Cheapest priced copy (Aetherdrift): $0.35 at Card Kingdom, near mint, their price list as of .
Brightfield Mustang 
Creature — Horse Mount · 3/3 · Common · Aetherdrift · #5
Whenever this creature attacks while saddled, untap it and put a +1/+1 counter on it.
Saddle 1 (Tap any number of other creatures you control with total power 1 or more: This Mount becomes saddled until end of turn. Saddle only as a sorcery.)
Legal inCommanderBrawlStandardPioneerModernLegacyVintagePauper
1 printing · $0.35 to $0.49 at Card Kingdom
| Set | Number | Rarity | Card Kingdom | Foil |
|---|---|---|---|---|
| Aetherdrift | 5 | Common | $0.35 | $0.49 |
6 rulings from Wizards of the Coast
- 7 February 2025You may activate a permanent’s saddle ability even if that permanent is already saddled.
- 7 February 2025An ability that triggers when a creature “attacks while saddled” will trigger only if that creature was saddled when it was declared as an attacker.
- 7 February 2025“Saddled” isn’t an ability that a creature has. It’s just something true about that creature. It won’t stop being saddled until the turn ends or it leaves the battlefield.
- 7 February 2025“Saddle N” means “Tap any number of other untapped creatures you control with total power N or greater: This permanent becomes saddled until end of turn. Activate only as a sorcery.”
- 7 February 2025Creatures with saddle can attack or block as normal even if they aren’t saddled.
- 7 February 2025If a permanent becomes a copy of a saddled Mount, the copy won’t be saddled.