actually I had no part in the creation of that amazing boss character.
Credit goes to a creator named N64mario
He's moved on from MUGEN coding for the most part & is currently experimenting with the Mega Man engine to make a full-game using that.
you can get the Boss Mouser and many other creations at his mugen site:
http://gcnmario.free.fr/mugen.html
I'm still working on Donatello guys. If you wanna contribute any resources that can further his progress don't hesitate to send me a pm