The save file for the game now includes a category for slime girl? data miner leak lol? Also if you try to use console command to summon a slime girl you get weregirl. So clearly there's a placeholder in there.
Others Nakara [v0.6] [Redspike]
I believe there is the gargoyle scene from the soul prison area where they use their tail, other than that I dont beleive so.
Every scene in Soul Prison involves your butt getting fucked iirc. I think if you face Beholder, she fucks your mouth when she cums too.