ngl ts!underswap sans is really one of the smartest sans out like instead of giving up and taking the hit he just pertend to give up just to bait you with an carboard cutout
fun fact: you can be at love 7 by the end of the ruins, and love 10 on late evacuasion ( neutral in ruins and geno in starlight isles ) how? love is obtained by using pick on to increase loux xp to 22, then killing 2 when you are at 19 killls. though you need to kill the ruined knights before as there is only a maximum of 15 louxes you can kill before them, so leave 1 room with a double encounter and come back at 19. How to get love 10? Spare the ruined knights, kill 21 louxes, kill asgore, kill beenard and the sun enemy. kill all of the canine unit, and get 17 wood works ( kill 15 and get a double ) this should put you above love 10 before sans ( in evacuation )
It's more of a hard mode material. Basically, instead of actually starting a fair fight, Asgore just gives a long speach about your actions, grabs his trident and oneshots you without giving even a slightest chance to win.
Sans has GUARANTEED damage at the end, even in normal undertale, although I'm not sure how he slams us in UNDERSWAP, I know he slams us in the corridors in vanilla undertale, but here, he's... something