Okay, so I may have been asked about this by an anon a bit ago, which I didn’t answer due to not being able to find what they were talking about (Sorry Anon), but holy crap I just stumbled upon this and I had to show you all.
It’s basically a custom Team Fortress 2 map, with an original Cuphead-styled boss in it, using all new animation, and a bunch of neat new mechanics! As an April Fools mod no less!
Monsters and Stuff 