This is just a repost by the wayDEF files are mostly definitions. For characters, it defines the name, author, and included files. In the data folder there areselect.def - defines characters in the select screen and where/when you fight themsystem.def - defines how the menu screen, versus screen, and character select screen should look likefight.def - defines how different fightfx and lifebars should be used/placed during a matchSFF files contain sprites, for characters it obviously cotains any and all sprites for the character. There are also SFF files in the data foldersystem.sff - contains sprites for menu screen, versus screen, and select screenfight.sff - contains sprites for lifebars and other elements such as pre fight textfightfx.sff - not necessary if every character uses it's own fx, but it contains sprites for various hitsparks and such, for a complete game it is advised that every hitspark be put here.AIR files contain information about animation times and collision boxes. Every character has one and in the data folder fightfx.air defines the anim times for everything contained in fightfx.sffSND files contain sounds, not much to explain.And files that only characters have:CMD files define commands and usually contain State -1 in it's entirety. Otherwise they are treated exactly like CNS filesCNS files are where all (or most) of the programming is at. You can read the mugen docs to learn more.ST files are just renamed CNS files.ACT files are palettes for a character. It consists of 256 3-byte color entries, where each byte defines red,green,and blue respectively.NEWFNT files are fonts that mugen uses to display text in the main menu, select screen, and in fight the names of the fighters next to the lifebar. Put simply it's just a PCX image of the various letters compiled together with a text file describing where each letter/symbol is located on the image.Refer to the helpful mugen tools sticky for how to edit these files.