Plum Pudding

Fakes cheerfulness to ingratiate herself to humans with power over her in order to avoid punishment, usually unsuccessfully. Has low self-esteem due to repeated failings at basic tasks during her training period as well as during her life before slavery. A little bit dumb. Exceedingly clumsy and incompetent. Has become resigned to being punished for her failings, which she sees as inevitable. Resents other slaves who she perceives as being more talented than her at being a slave. Hates being a slave, but hates her own perceived uselessness as a slave much more.

Ponies escape the destruction of their world. However, after fleeing to another world they end up as slaves.

Increasing the world population by almost a billion aliens from one second to the next has predictably complicated outcomes as every country on the planet gets thrown into an immediate crisis.

Treat them as refugees? Every government and economy would instantly collapse under the strain. Ignore them? Impossible. Open hunting season? Too cruel.

As the UN bickered, fragmenting as each country proposed or objected to different solutions, one less reputable country decided to take their own problem in their own lands into their own hands.

The solution was obvious, elegant even, in a twisted way. They aren't human, so they can't have human rights. They aren't simple animals, so they aren't covered under animal welfare laws. The government and country can't survive the strain of caring for them as refugees. So don't treat them as refugees, treat them as a resource. Offload their care and keeping on the civilian population and economy. That country quickly enacted laws that all ponies belonged to the government, at the moment, and put out a small but decent sized bounty for every pony turned in, as well as steep fines for housing them without turning them in. Then they turned around, trained them hastily in their new roles, and sold them back to anyone who wanted to buy at a small profit, paying for both the bounties and the limited care they had to provide between a pony being turned in, hastily trained, and sold.

There was international outrage of course, but it was heavily muted by every single country trying to manage their own crisis.

And as days passed and other less reputable countries saw that it was working, that the country in question wasn't collapsing from the strain like everyone else, and the government was even making a small profit off of it, they started following suit. Eventually countries that weren't shitholes started following suit. First out of desperation, and then, as it kept largely working well, because it was the only solution, a terrible solution, that seemed to actually work.

Plenty of countries, out of sheer abhorrence for the return to chattel slavery, refused of course. A good number even managed to survive without the government collapsing, though their economies are in the toilet and large ghettos of ponies spring up everywhere in them, with at best strained relationships with the original population of those countries who had to fund the massive effort through insane tax hikes that the government keeps telling them are temporary but never actually puts a date on.

And so, just a couple months after the world was rocked by the arrival of over 900 million ponies and other creatures, things have settled down to a degree. The vast majority are slaves. Some are free and either living on the run in a country where they are declared by law to be property, or doing their best in some uninhabited wilderness with nothing but the possessions they could carry in the saddlebags they packed before going to one of the portal sites, or scraping by in a ghetto in a country that is itself now barely scraping by entirely due to their existence.

And the ponies? Well, the massive last minute coordinated portal spell to evacuate as many as possible as quickly as possible was supposed to place them in groups of a few thousand randomly across the landmasses of an uninhabited world. Ending up on a world with more than 8 billion already living on it was not in the plan. What went wrong? Well, no pony actually knows, but in the insane rush to save as much of their world as possible the order to form a division of mages to work on the "uninhabited" component of the largest ritual spell ever constructed, with hundreds of interlocking components, each one as complicated as any attempted before, literally slipped off of a desk and ended up behind it. With every existing division's liaison reporting completion no final checks were made, as time was running out. The spell went off, and the ponies and what other creatures that lived in or that managed to reach their lands in time found themselves on Earth.

Treatment varies from country to country and owner to owner. Most of the government processing/training facilities are hastily converted office buildings, abandoned factories, little used sports stadiums, and any other cheap, large, and available space. The training given is very basic and over in a week or so in most cases, though it varies from place to place, and mostly consists of going through what's expected of them and exercises where they play out examples of roles they might be expected to fill, which mostly amounts to domestic servitude and commercial service jobs. Most places either legally require or strongly prefer that ponies wear a collar, mostly to differentiate between those that have been turned in and registered and those that haven't or that are runaways, though modern first world countries often chip them with an RFID tag as well registering them in a database with their name, face, side profile, and cutie mark, and give them a unique registration number. Most of the time the collars in question are whatever the government could get cheaply in bulk that would fit, usually textile dog collars due to similar sizes. Exceptions are made for aggressive troublemakers who often have thick leather or even metal collars secured with a lock. Leashes as well are usually simple dog leashes, with troublemakers getting chain dog leashes or actual chains.

How owners treat ponies, and what expectations are placed on them, varies widely as well, from country to country and person to person, or company to company in the case of ponies purchased by companies. Some are bought as essentially live-in maids, gardeners, cooks, or nannies for children. Others as living sex toys. Others are companions, sexual or otherwise. Others still work in every position from secretary to car mechanic's assistant to brothel worker to sales clerk to waitress to barista to factory worker.