Laughing and having a wonderful time.

As previously mentioned in the backstory about Amore, she had been going to eliminate Discord before being put on ice by Sombra, leaving the threat of Discord still at large in Equestria. With no other options left, a number of ponies sacrifice themselves in a ritual that combines all of their mass and souls together into two entities, which become Celestia and Luna. Exact details are still rough, presumably they maintain mortal pony forms and put much of their effort into trying to prevent the world from being invaded by other eldritch entities, having seen the havoc even one with lesser powers such as Discord was capable of, but when their subjects begin to make contact and transform themselves they're able to drop the act and make their true forms public knowledge.

Full res available here: https://derpibooru.org/1286375

My Little Pony as a whole is owned by Hasbro.
Original art by  mr.pink, colors and such done by me.



I can't help but imagine the magic holding them together running out and leaving them as limbless torsos.



The boob and butt emphasis would normally be the other way around.