Once you have downloaded a character file (usually in a ZIP or RAR format), follow these steps to add it to your game: Unzip the character's folder.

The most popular hubs for finding and downloading free M.U.G.E.N characters include:

Open the data folder, find the select.def file, and open it with a text editor.

The largest repository of characters, stages, and screenpacks.

Copy the extracted folder into the chars directory of your M.U.G.E.N installation.

Often used for downloading the core M.U.G.E.N engine for Windows. How to Add Downloaded Characters

The original developer's site, which provides the engine and base documentation.