the mansion has stuff to easy remove it
"easy" might be relative here. It isn't if you don't already know about it. I've done everything I can think of in the mansion, and can't figure out how to progress further, let alone undo that transformation. I've played for a minimum of 20 hours, possibly as much as 30.
At this point I'm just going to start a new save because while it might technically be possible to continue this playthrough, for all practical purposes, I've spent over a day trying to figure out how to get rid of it, and can't. I like to believe that I'm relatively intelligent, and that my experience would be at least somewhat representational of what most new players would experience. Frankly, if you get infested with the squidrabbit before knowing how to get rid of it, it's better and easier to restart the game then try to bruteforce some obscure method the game hasn't even hinted at. And ALL progress I can think of is locked behind getting rid of it.
Edit: to be clear, this is my first playthrough. I was infested Day 1, nearly immediately without exploring the other side of the lab. (I was able to run from the other creatures, even past them, so why not this thing? I didn't expect it to essentially game-endingly difficult to get rid of, let alone even semi-permanent.)