From Readme:
I've been planning to make a proper Doomguy character for Mugen for a long time, because what we had previously were pretty lame. Since porting a character from an FPS to a Fighting engine is not an easy job, it took me much time to collect the proper material. Especially the needed sprites to make the necessary moves like crouching, jumping, guarding, etc. This was one of the most time consuming part of the whole project. Besides making the hyper moves and fatalities of course. Luckely, thanks to the fact that Doom have a huge community, it was possible to make this happen.

It worth to mention that this Doomguy is not based on the classic Doomguy, but the Doomguy from Brutal Doom mod. And just like that, this is a highly configurable character, so you can choose from several options. Like if you want to hear one-liners, or you prefer the classic, silent Doomguy. You can choose between walk and weapon sounds, armor level, AI level, enable gore janitor, or you can turn off fatalities.