Did you have to do something special on the source based install to get the experimental packages? When I did my sourced based install I ran the following:
sudo ./retropie_packages.sh mupen64plus
As far as the rom folder goes, did you just create a folder on your own called mupen64plus or was there automatically a folder with that name? I can create a folder easily enough but I don’t know how to tell mupen4plus where that folder is. I have been going through all the configuration files I can find for the emulator but I haven’t found any reference to a rom directory.
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