This website is best for modding: https://turbowarp.org/673821644?fps=60&hqpen Learn how to use this engine here: https://youtu.be/zGeXtvg0U2A Go here to convert beatmaps into readable files: https://cabalex.github.io/fnf-song-converter/
Credit All, especially to chucky_lee and cabalex for base engine, plus Xploshi for menu theme I can't make a Marvelous tag for technical reasons
