How to Fix Common MUGEN Errors

Most MUGEN crashes are a wrong folder name, a 1.0 char on 1.1, or the 2GB memory cap. Work down this list before you reinstall the engine.

Error loading p1 / out of memory

MUGEN 1.1 is 32-bit. It dies around 2GB of RAM, which a couple of HD characters will hit. The message is often "Error loading p1" even when player 2 is the problem.

Apply the MUGEN 1.1 4GB patch to mugen.exe, then retry.
Or move the roster to IKEMEN GO, which is 64-bit and does not have that cap.
Wolf_Stak's Son Goku documents this on the listing: 2700+ sprites, 1.1 only, patch required. That is the usual HD case, not a bad zip.

Character does not appear on select

select.def line is not the folder name. Pocket Bowser fails if the folder is bowser.
Extra directory. The zip extracted to chars/bowser/bowser/. Move the inner folder up.
You edited the wrong select.def. Screenpacks sometimes ship a second one. The engine reads data/select.def unless system.def points elsewhere.
The line sits above [Characters] or below [ExtraStages]. It has to be in the characters block. See select.def.

It boots on 1.0 and dies on 1.1

Elecbyte 1.1 is still a beta (1.1b1). Older WinMugen / 1.0 conversions trip on palettes, localcoord or OpenGL. That is expected.

Keep a 1.0 folder for those chars, or load them in IKEMEN GO, which reads a lot of 1.0 work.
Do not mix a 1.1 stage (zoom, OpenGL) into a 1.0 install. Chikara Tournament is 1.1 on purpose.
Full comparison: 1.0 vs 1.1 vs IKEMEN GO.

Failed to load .sff / .air / .snd

The .def still points at filenames from the author's PC. Open the character .def and make sure every path is relative, inside that folder.
Spaces and parentheses in the path can fail on older builds. Short folder names are safer.
You copied only the .def. The sff/air/snd have to sit next to it.

mugen.exe vanished or will not start

Windows Defender flags a lot of MUGEN builds. Restore the file from Virus Protection history, then add the engine folder as an exclusion. Scan the character zips separately; the engine itself is not a download from a random host if you used the MUGEN or IKEMEN GO listings.

The "game" is one huge .exe

Older full games were packed with Molebox. You cannot add those characters to your own install until you unpack. DE-MOLE-ITION extracts the chars and stages. After that, treat them as normal folders.

Read the log

When MUGEN crashes it writes mugen.log in the engine folder. The last "Error" line is the file it could not load. IKEMEN GO prints to the console and to a log in its folder. That is faster than guessing.

Debug mode (Ctrl-D in 1.0/1.1) shows hitboxes and the AI switch. It will not fix a missing sff.

Tools that actually help

4GB patchFirst fix for Error loading p1 on 1.1 with HD chars. VselectDrag portraits on the select screen so you are not counting commas in select.def. Fighter FactoryOpen a char that will not load and see which file the .def expected. IKEMEN GOWhen 1.1 is the bug. 64-bit, same chars folder.

FAQ

Should I reinstall MUGEN?

Almost never. The engine is fine. The char, the path, or the memory cap is not.

Black screen for ten seconds, then it plays.

HD first load. Wait. If it never returns, that is the memory error, not a slow disk.