There was an old maractus animation of her riding with a smug expression on her face. There was an internal view where her vagina walls had cactus shaped barbs or flesh shaped thorns. It was pretty good one of the better animations of maractus But now I can’t seem to find it any where?

There is topic for this:
https://e621.net/forum_topics/23835

Based on your description, I think it is the following post:
https://e621.net/posts/4142589

I might have found it on a different website. It seems to match your description:
https://agn.ph/gallery/post/show/428804/

As a side note, you can look for deleted images by adding status:deleted in the search. You won't be able to see the actual image, but it can help when tracking down a work from a certain artist.