Ever since the monsters began living on the surface, Sans had begun acting strange. From violent mood swings to out of character violence and depression, it was soon obvious that something was wrong...very wrong...but what? Unofficial Theme X3- /watch?v Ax18frb9ENo

While he is waiting for Undyne to come to Snowdin, Papyrus goes to Sans's Snowdin sentry station and learns the reason for his existential depression. After all, it doesn't matter if Sans tells him. It's all going to be reset anyway, won't it? (Oneshot, loosely based on "Waiting for Godot")

Sans's family is a lot bigger than he thinks. (Insp. by this comic: sylphee. /post/135223041721/ tfw-depression-mucks-up-your-sense-of-time-resets) (Part of the Cheer Up the Skeleton prompt week by teffyjeffy on Tumblr)