I like the mechanic you chose to explore, and I think you explored it well with your level design. I could tell that each level built on the last one, which provides a great sense of progression. However, I think the levels could have achieved the same or better effectiveness if they were smaller and had fewer steps. One example of redundant level design was having to rotate the ghost in a 3x3 room. I know I can do it, and I've done it before, but I had to do it several times in different levels for some reason.
I might just be dumb but it took me a few minutes on my first encounter to figure out the technique for getting both the fox and the ghost past a ghost wall. I think a small level with literally just a ghost wall would have been interesting on its own, because it's a deceptively simple setup with a somewhat tricky solution. But once you know it, you know it. Figuring this out was my favorite part of the game. Here's a minimal example of what I mean:
#=Wall, .=Open Space, F=Fox, G=Ghost, W=Ghost Wall, P=Portal ######### #.F.G.W.#P #########
The last few levels were hard, but not satisfying generally. I didn't feel smart after solving them, just more and more discouraged as they got more complex. I almost gave up a few times.
The last level wasn't super satisfying, which is a bummer. I didn't exactly make any insights to find the solution, it just felt like I was feeling around blindly and accidentally found the solution. The symmetry of the level kind of served as a red herring which helped to hide the solution, which is neat I suppose. I don't know how to describe it well, but it basically feels like the difficulty came from the complexity of the level and not the profundity of the mechanics. Anyway, once I got past the hard part, I instantly knew I could do the rest, but actually doing it was kind of boring.
The multiple ghost mechanic overall feels a bit contrived and unintuitive, and didn't feel fully explored. I feel like there's a lot of promising design space still left to explore with just the single ghost. Great work and I hope you decide to explore this design further.