As NSFW Tumblrs are basically inaccessible, here's what I've been able to put together:

Original link was https://batyastudio.tumblr.com/post/156088337917/movie-1-mlp-xxx-sex-is-magic-celestia-amused

As NSFW Tumblrs are basically inaccessible, I searched for a download link and found this: https://www.tumbex.com/batyastudio.tumblr/post/156088337917
That link has the cover art for the video, a page of screenshots, and links to the patreon, places to find the video online, and a megaupload download link.

Megaupload link copied from the tumbex thing listed above: [link]
I don't know if the megaupload link will work for others, or if it was created just for my session, so I recommend you check the tumbex link instead.

The video is 179mb in the .rar file you get from Megaupload, and decompresses to a 183mb mp4 file that's 2:31 long.

Patreon link: https://www.patreon.com/BatyaStudio

Bideo is 3 years old, so it come out some time in 2018.

Naughty Machinima link: http://www.naughtymachinima.com/video/22218/mlp-xxx-sex-is-magic
The PornHub link was flagged for "verification in accordance with our trust and safety policy".

Credits:

DisCodeR — Chief
DominotheCat — Animator
Skykliker — Poser
Audiodude — Sound