Papyrus wears his Beta design due to an ouchy Alphys gave him (large bite wound) Papyrus gets splitting headaches quite often and prefers to stay in darker environments to shield his eyes from the light (photophobia)

Sans had a psychotic breakdown after being denied from the royal guard for the last time. He was sent to an institute and put in a straightjacket, but was able to rip his arms free and escape. Mostly rearranges the same puzzle over and over alongside incoherent mumbling.