The Information Of That Punny Comedian :)
This swap sans is stronger when he is in the genocide timeline, he can also use the advantages from his training which gives him more speed and reflexes to dodge, skills learned from his friends, the energy and stat increase, DT getting stronger and not melting thanks to his knowledge of mixing a trait with another one which is PT, Him using items to heal or increase some stats for himself, and him being able to use the reset button after making the human give up, though he is not the final boss in the genocide run, that would be toriel since he told her to absorb the human souls.
Also, he is observant so while the anomaly is doing their geno run, he goes around the whole underground to announce of a dangerous human, that’s why their are only a few monsters to be found in the underground.
On pacifist well, its already up there but ill give you info.
on the date with sans or hangout with sans, he will take the protagonist to either grilbys, his room or to waterfall which has the glowing rocks with his telescope, though he is going to say that he is not into dating the protagonist cause he already has a girlfriend ( which is alphys )
He is very great at cooking, he also loves to party but he sometimes cancels it or get’s only a few visitors because of reasons.
in the end of the pacifist run, alphys and sans will be found kissing or nuzzling.
Since i only drew the gen and pac run, its time for the neutral run info
Sans will only get triggered on the neutral run if you kill papyrus or alphys
Killing Papyrus: Neutral Run And Genocide Run
During his battle he can’t be killed in the neutral run, since when he spares the protagonist and then attacking sans, papyrus will be the one who will take the damage by blocking the hit from sans, this will cause sans to enraged that he will fire blasters and throw the protagonist on any wall, he will then flee from the fight, after that, everytime the protagonist encounters a monsters random blue bones and bones will try to hit the soul, that will happen in the genocide run too after killing papyrus, he will use G blasters with blue and normal bones everytime a monster is encountered, he will also sometimes heal some monsters by throwing random items at them. he will do anything to avenge his brother.
Neutral: On the judgement hall, he wont fight the protagonist but will try to tell them to use their powers for good and reset to bring back papyrus, saying yes will cause him to kill the protagonist and say “ if we are friends, please bring back papyrus” going back and not doing it will result of him not being there in the judgement hall. saying no to him will make him tell the protagonist that they should use that power with responsiblity, he will then leave the area.
Genocide: On the judgement hall he will fight the protagonist and wont be fair about it, he will use different patterns, repeat his special attacks, use other soul modes or even mix them, dodging 4 times longer than classic sans, can block some attacks, and beat up the protagonist using his final special attack which is blasters and bones everywhere, the final is he punches the soul repeatedly instead of throwing it everywhere, thats not just it, he has 3 phases which makes him a powerful swap sans.
Killing Alphys: Neutral And Genocide Run
After killing alphys in a neutral run, he will fall into heartbreak and regret of not being able to save her, he wont be intense unlike killing papyrus in a neutral, he wont appear anywhere in the underground after a neutral run, the only place you can find him is his home which checking the narrator will say * You hear crying and words you cant describe *( this can happen also after killing papyrus on a neutral run after leaving snowdin and coming back to his house without encountering a single monster ) standing in front of the door for too long will make papyrus open it and tell the protagonist that sans is not well right now, he will then explain it to the protagonist why he is upset, which the protagonist will say the regretted it or their actions are justified, saying they regretted it will cause sans to go to the door and tell the protagonist that what they did was self defense but the could at least talk things out with her, saying its justified will make sans tell the protagonist that they are right but alphys didn’t want to fight either.
he will then tell the protagonist that him and alphys only joined the royal guard so that they can get some physical and stat increase, not because they wanted to kill anyone, but since monsters wanted to leave the underground alphys has no choice but to do her job as the leader of the royal guard so the hopeless will have their hopes up, he will then explain that she has gone through so much that he tries to help her, he will then go back inside the house into his room, you cant unlock the room since it will be locked.
in the judgement hall sans wont be there
Sans will help alphys on the genocide run by healing her with some items and using blasters and bones to attack the protagonist, you cant fight him since he is only their to help alphys, he will be hidden during the fight, after killing alphys there will be a rage of blasters blasting at the soul of the protagonist.
It will be the same in the judgement hall
(PT stands for patience, also this is my take of underswap so the PT ability to not let monsters melt is an idea of mine :)