Because I do. It's a really fun free fighting game for PC where you can insert and/or make your own characters, stages, etc. It's such a shame that there's not enough Nanoha characters for it though as the only ones that have been made are young Nanoha, young Fate, Signum, young Hayate, Vita, and Subaru.... So, I created a group tasked with creating a MUGEN 1.0/IKEMEN GO Plus full game based on the third season, StrikerS: https://mugenarchive.com/forums/group.php?groupid=148
BTW, if you want to join this group, you must first create a account for the MUGEN Archive (the website the group's on).
I think my classmates swapped characters of this game when we still used floppy discs. I'm surprised Mugen is still around.
Do you need sprites? i was working on some but I don't know how to implement them into Mugen of all things...I didn't even know it still existed O.O
The MUGEN community is still thriving but Electbyte (the creator of MUGEN) hasn't made a update to it in years.
However, there's also an open source MUGEN clone called IKEMEN GO/IKEMEN GO Plus if you want to try that instead.