First off thanks to CykaBlyatintensifies and vaultdwellerdead for the kind words, and yes sans is a weird boi indeed.
This chapter I'll just explain sans upgrade or aka sans 2.0
Sans has pretty much the same stats 1/1 hp, 1 atk and 1 def.
One hit and he dies, bum, dusted.
But now he has obtained a new power out of this new world known as Aura! A manifestation of the soul that protects you from damage.
But there is one problem, sans soul is really weak, and by itself it would not be able to create aura, so to fix this, the aura uses sans own magical energy to manifest itself.
And while sans may be the weakest enemy, magic is something he is great at and now his magic surrounds his body and makes him incredibly resistant which means he wont die if he gets hit.
Now the only way to kill sans would be to shatter his aura completely which would also drain him of all magic, the problem being that sans doesnt get tired using magic, he only gets tired if he needs to evade and his magic recovers really quickly thus also recovering his aura, if you manage to hit sans it would drain his aura a bit, now the problem is on how to him him again before he recovers it.
Aura also gave sans those other neat perk it gives other aura users Like making his bone attacks stronger and his blasters deadlier It also made him stronger hence being able to punch emerald in the shin and sending her flying.
Sans also gained a semblance, one that got mixed with his magic of another world, and this semblance is called Judgement.
A passive type of semblance that affects anyone that has been affected with sans KR or KARMA karma drains the health of the victim like poison depending on their sins and leaves them feeling heavy and reminds them of said sins, KARMA Affects other's aura by corriding it slowly and the more you get hit by sans attacks the more KR you get and the faster it drains your aura.
If one manages to avoid getting hit from sans attacks for a while KR will slowly dissapear but if your aura is broken KR will now target yourself and activates Judgement.
Judgement works like KR used to but to an extreme level, not only reminds them of their sins, it makes them confront them, creating illusions of your past sins that start to damage you directly and recreates past places.
The illusions cannot be hurted since they arent really there, but they will hurt you working the same way as KR did before working as poison damage but in an extreme more painful way.
Ofcourse sans can choose if he wants someone to be affected by Judgement and make it work like normal KR, he also can't see what the ones affected by Judgement see, Judgement and KR also only affects those who had sinned on their life so for example it would only affect two memebers of team RWBY or only one depending of certain circumtances.
Only those that pass sans judgement can beat his Judgement...does that makes sense?
Sans would normally do what all monsters do and attack the directly the soul of the one who he fights against but in this world that could be lethal to others since in this world they can't heal their own souls like frisk could in undertale with magic items.
So instead sans attacks them directly and while its true that if he fought against someone who hasn't sinned before he would have a harder time, he could still come on top, low stats or not getting impaled by bones and hit in the face with a laser will hurt.
And that is how our old pal sans has been upgraded! Now he is more than ready to take on remnant!
Not that he wants to but i wont let him sleep lol