Anon describes a board game from home, and Twilight arranges a game night to recreate it. This proves to be a greater threat to their friendship than anything they have faced.
Equestria is facing a potential crisis involving distorted reality based on cognition. Celestia tells an old friend, who has just the solution for her...
Henry has a body count in the dozens and nothing but questions about his past, but most of that is put on hold when he literally crashes into some weird horse dimsension.
Equestria has resources not found in any other dimension, so of course an alcoholic, mean-spirited scientist would get in on that and drag his grandson along for the ride.
A collection of documents pertaining to SCP-7663, including Experiment 7663. WARNING: LEVEL █ ACCESS IS REQUIRED TO VIEW THESE FILES. UNAUTHORIZED ACCESS CAN AND WILL RESULT IN DISCIPLINARY ACTION UP TO AND INCLUDING TERMINATION.
So, stop me if you've heard this one: a changeling queen, a homicidal flower, an extremely intelligent meglomaniac, a much less intelligent metal ball, and a mute sociopath are stuck in a house together in Ponyville...
Pinkie Pie meets some new friends, and they bond over silly friend things, like cooking, telling jokes, racking up debt, and calling the fire department.
Twilight visits her human friends again, only to find that they're currently in a large-scale war at the moment, and are caught up in the middle of it..
After a spell apparently does nothing, Twilight wakes up in a completely different place, with a gun, some bullets, a tape deck, headphones, and a horde of killer robots coming after her.
Doomguy, Duke Nukem, BJ Blazkowicz, the guy from Marathon, Chexguy, the mage from Heretic, the cleric from Hexen, and Quakeguy all stumble into Equestria. Hijinks ensue.
Nightmare Moon won in the pilot, but then she's overthrown by Mental, so the ponies need to call in "Serious" Sam Stone to help them overthrow this new evil ruler.
A group of robbers end up at ground zero of Earth and Equestria having portals opening between them. The robbers blend in with the crowd and bide their time; at least, until they decide that Equestria has some nifty things to steal...