Halo:CE MCC - “HMBI Classic” Mod Campaign - The Library (The Crypt - Normal)
Found this on steam workshop; seems to be a 2011 era release for the original pc version of CE. It has some wild texture - weapon - enemy changes and is certainly interesting. The most fascinating thing is that when you crouch, you move at 2x or more speed. This also allows you to essentially slide up sloped or curved ledges
I use this to skate by most of the tough parts in this level.