Refuse the request

"Then you’ll earn your keep as a dirty pony" he says with anger. "I will find a way to earn more money with you, you will see"

After that day, the shows are bad but the "after-shows" are worse.
Goblins pay extra to "ride the new mare" You’re whipped for stumbling or disobedience, then ****-fed glowing red potions that heals you enough to endure the next day. The audience adores your suffering, and some of them want to ride and fuck the mare in public.
For special shows, they take off your plug during the show and make you empty your bowels in front of everyone. The disgusting spectacle degrades you even more, and they laugh looking at your embarrassment and disgrace.

After some time, you are so broken, that you lose any hope, you just want to die, but the goblins keep you alive using potions and treating your wounds.
You have a terrible long life, full of disgrace and suffering, and you never returned to your world.

Bad ending
Goblin ponygirl show ending