chars/Goku/Goku.def For a character in a subfolder like chars/DBZ/Goku/ :
Result: MUGEN/chars/Goku/ (Inside: Goku.def , etc.) Go to MUGEN/data/select.def . Open it with Notepad. mugen install characters
Find the section under [Fight] (usually near the bottom). Add your character on a new line using this format: chars/Goku/Goku