Hey - sorry you experienced issues with the mirror character. I hoped I had ironed a lot of the bugs out. Sadly, frame drops and other performance issues can affect the mirror characters and throw them out of sync by a few millisecond. That can be enough to make them overstep a button or miss a jump. There are some changes coming to itch.io which would allow us to upload a better performing web version and, after the jam is finished, we were thinking of uploading a binary version too which would perform better as well.
but, thanks for playing it despite these problems :)