Board Thread:General Discussion/@comment-32710969-20181206223055/@comment-43785098-20190918042715

Stat-wise, Sans is the easiest, having the worst attack and defense, but like what User1204 said, it is because his attacks disable I-frames. You can also (somewhat) negate this effect with the Cloudy Glasses and Torn Notebook, which give you a little bit of extra I-frames. Karma isn't poison, in fact, it helps you. I think story-wise that Karma is all of your LV catching up to you. Sans, being a mysterious and powerful monster, takes advantage of your LV and uses Karma to aid him in his fight, but in gameplay, it just disables you from getting owned by the lack of I-frames. Sans is also powerful due to his manipulation of the arena, a power that only a few other share, like Muffet or Papyrus. He also dodges, knowing that your attack will one shot him. He even states that he can control the length of his attacks, explained by his final "attack".