Creating mugen characters from scratch is definitely a pain. There are tutorials to do them on youtube, but it'll be time-consuming for sure.
It's much simpler to modify an existing Mugen character. The tool you need is called Fighter Factory 3 or whichever version you want to pick, and all you need to do is just download a character you want from Mugen, and just change a specific part of that character to suit what you want like their voice lines, attack special effects etc. It's tricky, but it's easy to get the hang of once you get used to it.
