Party Poopers

Party poopers:
No one knows where they came from.
Unlike normal changelings, this breed of pony-like bugs tend to have golden colors and holeless bodies. They are much more aggressive than normal changelings too, always going to attack, as they don’t have a queen to follow.
Their holeless bodies might seem too heavy to lift with those weak wings, but they’re much stronger than they look.
The biggest difference between the two breeds, however, is their food habits. While Changelings ate love, and were weak to it (Until reformation), Party Poopers eat “Fun”. It’s a much harder concept to grasp, but that’s probably why ponies find it much more terrifying. It doesn’t matter if you’re happy, sad or angry, you can always be having some kind of fun.
They also appear to have no emotions, and are immune to emotional outbursts, opposite to Changelings and their weakness to bursts of love.
A pony without “Fun” seems to have no emotions. They are unable to care for others, functioning only on a survival approach. It is possible to “Go back”, as some have done it, but nobody knows what is it that allows them to “Go back”.
They appeared ten years ago, two weeks after the Big Disappearance. They got their names after ponies realized that ninety percent of the time they attacked parties. From there on, parties became extremely private and ultra-secure things (Gunner’s Night Club might have been a little careless in this regard).
The big domes were constructed in a few months, as all the ponies managed to work together. Manehattan, Cloudsdale, Canterlote and Baltimare managed to build them. Fillydelphia, instead, built a big wall with some incredible air defences. Somehow, they’ve been able to hold back the Party Poopers.
All other cities in Equestria have fallen. The Crystal empire dissapeared like it had done a thousand years back. Appleoosa and all the other towns were either destroyed or evacuated to the big cities.
Ponyville was obliterated with all its population. Nobody knows what happened there, and nobody dares investigate.
Since then, ponykind has been living inside their domes, only mercenaries daring to go outside.

Big Disappearance:
The day all four princesses of Equestria, along with their closest friends and family vanished. From that day onwards, the Sun has been hanging in the west of equestria and the Moon at the east, creating a perpetual day/night.

New information:
Manehattan has fallen too, its dome swarmed by Party Poopers.
Party Poopers find it very difficult to walk. Their legs seem to be way heavier than they should to facilitate capturing ponies, but this is a disadvantage in the moment they lose the ability to fly.
They appear to have help from a pony?

What has the future saved for the future of Equestria?