Maybe thing of it this way..
Is the animation representative of an episode in and of itself? Give it it's own preview page with a long in the description.
Is the animation an extra or otherwise representative of an existing episode you're posting? Link in the description of the relevant episode.
However if you're putting a ton of time and effort in, you might want to give it it's own episode, even if it's the latter reason. You can get more visibility from being in the Fresh section that way. But at the end of the day, you'll gave to decide what flow you think represents the story best. Sounds like a great extra as tipping or patreon rewards potentially too.
(I don't have any links to other people doing anything similar, but I think it's a great idea if integrated well!)