Judgment

This video helped me a lot, but didn't explain everything in their description so I'll elaborate below:


Preparation phase:
unlock Tiger drop (counterattack that makes a lot of damage)
have several Die Hard Extracts, Blazing Barrage Extracts and medkits and assign them to your quick inventory (my personal preference, at first I tried using DLC extracts but they weren't as helpful as I thought)
Die Hard Extract is a great healing item because it uses itself automatically at the moment you would normally die and it has a generous timer, so there's plenty time to use it even before being low on health

Battle phase 1:
use Tiger drop and dodge Amon's grenades
This phase is quite easy, most annoying part is if you aren't perfect in using Tiger drop before every time Amon attacks from close range, he will steal your phone. That means not being able to pause and use other items except these in quick inventory
also make sure you fight in blue crane style before the next phase

Phase 2:
Amon switches to blue attack, use blue too and continue to counterattack him with Tiger drop

Phase 3:
Amon switches to red tiger style - immediately when this happens, switch to red too, otherwise he kicks you to ground where you can't switch styles meaning you're dead almost instantly
Keep using Tiger drop

Phase 4:
Amon switches styles often and has a shield
This is the part which gave me most trouble, because Amon basically stops getting damage before you kick his bubble out - when he's in blue style, switch to red for a short while, run towards a wall and do a kick attack - if you are succesful, his bubble shield is gone and now you can switch back to his blue style to avoid getting a lot of damage
This is the time to finish him off - quickly use a Blazing Barrage Extract to make a powerful BBBB combo. If you are fast enough, Amon is knocked out before extracts wears off. If he manages to change styles and gain his shield back, you'll need to redo these steps again (but don't try to kick his shield out when he is in red style, wait until he's back to blue)