wolfmanfp wrote:What does this mod do? I literally don't understand after watching that video.
It does exactly what it says it does: it gives every actor 0 mass.
Mass being a property that determines how affected by knockback an actor is - the higher, the more resistant to knockback it is.
So, the video shows you all that you need to know about what happens when you give an actor 0 mass: ZDoom unceremoniously breaking down as it tries to handle extreme velocities, with no sort of humor at all.
In other words, there's really no reason to do anything but give the video a glance, go "huh," and move on.