Dude, if you had a tutorial video on how to build this starting from level 1 through level 12, including tips and tricks and explaining how to play this build, it would get a ton of views.
Looks like he has at least 6 levels shadow monk, 2 fighter, rogue (arcane maybe), weapon is the duelists preogative (purple wyrm toxin) + ring of shadows
not op but 90% sure his build is this: 4 thief - 6 shadow monk - 2 fighter feats -- ASI -> dex, + (savage attacker? or two weapon fighting? idk) fighting style -- two weapon or defence starting stats s- 10 (for push saves) d- 17 (primary, hags hair here) c- 16 (big health pool bc will be under 50% hp) i- 8 (dump stat) w- 14 (secondary) ch- 8 (dump stat) weapons look like duelists prerogative and dolor amarus -- likely the dead shot for ranged slot build would likely be stronger if he went tavern brawler and no weapons? or monk 9 rogue 3 to wear weapons and use punches... not sure on the theorycrafting math here but my assumption is tavern brawler > stat sticks bc tb is BUSTED
I got inspired by these videos randomly showing up on my recommended and decided to try it as well and it has been the most fun I have had with this game and it isn't even close such an enjoyable playthrough, good stuff fellow monk enjoyer