Cheapest priced copy (Outlaws of Thunder Junction): $0.99 at Card Kingdom, near mint, their price list as of .
Caustic Bronco 
Creature — Snake Horse Mount · 2/2 · Rare · Outlaws of Thunder Junction · #82
Whenever this creature attacks, reveal the top card of your library and put it into your hand. You lose life equal to that card's mana value if this creature isn't saddled. Otherwise, each opponent loses that much life.
Saddle 3 (Tap any number of other creatures you control with total power 3 or more: This Mount becomes saddled until end of turn. Saddle only as a sorcery.)
Legal inCommanderBrawlStandardPioneerModernLegacyVintage
Not legal inPauper
5 printings · $0.99 to $21.99 at Card Kingdom
| Set | Number | Rarity | Card Kingdom | Foil |
|---|---|---|---|---|
| Outlaws of Thunder Junction | 82 | Rare | $0.99 | $0.99 |
| Outlaws of Thunder Junction | 324 | Rare | $1.49 | $1.49 |
| Year of the Horse 2026 | 1 | Rare | — | $21.99 |
| Outlaws of Thunder Junction Promos | 82p | Rare | $0.99 | $0.99 |
| Outlaws of Thunder Junction Promos | 82s | Rare | — | $1.79 |
10 rulings from Wizards of the Coast
- 12 April 2024“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.”
- 12 April 2024If a permanent becomes a copy of a saddled Mount, the copy won’t be saddled.
- 12 April 2024You may activate a permanent’s saddle ability even if that permanent is already saddled.
- 12 April 2024“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.
- 12 April 2024Creatures with saddle can attack or block as normal even if they aren’t saddled.
- 12 April 2024If the revealed card doesn’t have a mana cost (because it’s a land card, for example), its mana value is 0.
- 12 April 2024If the revealed card is a split card, that card’s mana value is based on the combined mana cost of its two halves.
- 12 April 2024If Caustic Bronco isn’t on the battlefield as its triggered ability resolves, use whether it was saddled or not before it left the battlefield to determine who loses life.
- 12 April 2024An ability that triggers when a creature “attacks while saddled” will trigger only if that creature was saddled when it was declared as an attacker.
- 12 April 2024If the revealed card’s mana cost includes {X}, X is 0 for the purpose of determining its mana value.