i must’ve watched this 10+ years ago on late night movie channels. I have vague memories of it but it has haunted me since. I remember that the bulk of the film was shot for lack of better terms like a side scrolling video game where you’re stepped back from the set and you’re sort of looking inward at it. There was a strange mouse man, I believe they went to hell at some point, a lot of underground tunnels and such. I also have a blackboard in my head. I know none of this makes sense but as a kid I was totally entranced by this and I felt like the movie dragged on for hours.
“Forbidden Zone”(1980)?
I think there was a color version also.
Here is a trailer from Youtube, they might also have the full movie there.
https://youtu.be/uUY1LRS23YM