It could be a short movie for streaming, like a Halloween spinoff. Maybe done for Universal's Peacock (tho I don't think anything can help that streaming service).
Like expanding on what happened in that Castle he was in.
I'm gonna take a wild and bold guess, it will be titled Luigi !!!!
PLease guys don't try to reproduce what I just did, it is dangerous and must be realised by a professional or at least someone that doesn't have much to lose.
After the success of the Mario Bros. movie Luigi’s Mansion was the first thing I thought about for their next project. I think it’d make a great animated movie.