Ash/Disbelief is the boss directly after Disbelief Papyrus in the Disbelief AU. He will use similar attacks to those that his brother, Neil C. Granger uses. Unlike regular Ash C. E. Granger, Disbelief Ash will use even more powerful attacks. He rivals Error!Sans and Ink!Sans in how powerful he is, but is not as strong as Neil.
Ash/Disbelief wears the same clothes he wears normally, except he now wears his brother's red hoodie instead of his own black one. His eyes go completely black when the battle is initiated. You cannot spare him, and he will not offer to spare you.