Jevil's attack power is much higher than Papyrus and therefore he can deal much more damage. His ability to teleport and shoot out ten large spade bullets gives him a big upper hand. Papyrus's magic guard is zero, which makes him highly vulnerable to any magical attacks from Jevil. Papyrus's blue bone attacks and other skeleton-based attacks can be avoided if one is sufficiently fast, which Jevil is with a speed of 34. Jevil's Carousel Attack and Chaos bombs make it almost impossible for Papyrus to dodge since its trajectory diverges up and down over time. Plus, Jevil can cause chaos in the arena, which can put undue psychological pressure on Papyrus. All of these factors give Jevil the upper hand in the battle, and hence he wins.