What is the of the screenpack you are trying to use?
Avoid random YouTube links with “download in description” – they often bundle broken configs. Instead, use these trusted sources: mugen 11 screenpack 640x480 work
If your monitor is high-resolution (1080p+), a 640x480 window will look tiny. Set Stretch = 0 in mugen.cfg . Upscale to Fullscreen: Set Stretch = 1 and KeepAspect = 1 . What is the of the screenpack you are trying to use