腐食の荒馬

An ability that triggers when a creature “attacks while saddled” will trigger only if that creature was saddled when it was declared as an attacker.

Creatures with saddle can attack or block as normal even if they aren’t saddled.

If 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.

If a permanent becomes a copy of a saddled Mount, the copy won’t be saddled.

If the revealed card doesn’t have a mana cost (because it’s a land card, for example), its mana value is 0.

If the revealed card is a split card, that card’s mana value is based on the combined mana cost of its two halves.

If the revealed card’s mana cost includes {X}, X is 0 for the purpose of determining its mana value.

You may activate a permanent’s saddle ability even if that permanent is already saddled.

“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.”

“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.