Fell Sans, much like every other monster in Underfell, is dark and edgy. Sans can be harsh at times. He often gets tired. He has an allergy to cats. He strives to be cool and collected. Papyrus tries to be cool and collect. He doesn't laugh, but snorts. He also "HMPH"s and sometimes goes "MWAH HAW HAW HAW!". He would oftenly gloat for absolutely no reason, if he’s being decent expect a humble brag. Papyrus can be obliviously considerate at times and can be awkwardly supportive.