You typically need three regional BIOS files for full compatibility: scph5500.bin : Required for Japan-region (NTSC-J) games. scph5501.bin : Required for North America-region (NTSC-U) games. scph5502.bin : Required for Europe-region (PAL) games.
After reading this article, you should understand that a "Mednafen Bios Pack" is not a magic file you download and forget. It is a responsibility. Mednafen Bios Pack
You can also set a custom path in mednafen.cfg : You typically need three regional BIOS files for
For the average user: If you choose to download a pre-assembled pack, verify each file’s hash against the Mednafen official documentation. And remember – emulation preserves history, but piracy funds none of the developers who made these consoles great. Mednafen Bios Pack