A quick 40 second short detailing how the final boss quick kill is setup. Will save 3-5 seconds compared to the normal method of defeating him. This kill was found accidentally by BrandonBlank and using his findings I was able to perfect a consistent method saving 2.5 seconds on the fight. With JaekRock's assitance, the kill has been extended to an additional 0.6-0.8 sec vs my original method. Feel Free to put this in your runs to better improve your times.

Alternatively, I have a more easier setup just 0.5-0.7s slower than the above method. To set this quick kill up, walk left as Neff is transforming until the screen pushes you back then crouch. Wait for the Rhino Boss to walk to you and throw 1 punch. After his punch, push him back a few pixels then crouch before he throws his 2nd punch. After the 2nd punch, stand up and let him kick you down, then as you get up hold right until you meet contact with the boss. That is where he will be instant killed. This setup is 100% guaranteed to work.