Help! Multiplayer!

[BlAzEfirE09]

What the hell is a bios file and where do I find one for Pokemon Emerald?

[Jale]

BIOS stands for Basic Input-Output System and it's for communicate the GBA hardware with the software (games). The BIOS files are not for specific games, but the console (GBA in this case). Since a BIOS file is copyrighted it's illegal to download it from the Internet and emulator-zone's policy does not allow that. I suggest you to look for it by yourself using search engines (Google, etc). Try several keywords like "gba bios".