If your arcade games work perfectly inside standalone RetroArch but crash with an "unknown romset" error through a launcher, your frontend is likely decompressing your files.
While these can work, they are often not ideal. It is always better to use standard, unmodified ROMs that match the current FBNeo DAT file. This ensures the best accuracy and performance.
Do not unzip these files. Leave them as .zip archives inside your ROMs folder. Summary Checklist for a Clean FBNeo Setup Why It Matters
To fix your ROMs, you need the official blueprint (called a DAT file) that tells your rebuilding software exactly what the correct ROMs should look like.
Changing mslug.zip to Metal Slug.zip breaks the emulator's ability to find the code.
What or handheld device are you using? (e.g., Windows, OnionOS, RetroArch Android) What is the exact version number of your FBNeo emulator? Are you trying to fix a single game or an entire library ?
