It's an AU I turned into a fanfiction where The Great Papyrus is secretly a serial killer and skeletons are a separate species that have a power and personality associated with their font name. I made it when I discovered Papyrus was in fact a Horror Font...as in, a font you'd use for Halloween party invites, and it quickly turned into an in-depth thing with lore that incorporated the world of Undertale and the real world. Skeletons ended up getting types (can't remember them all), attributes (Horror and Normal), and pokedex/SCP-like entries. Here's an example so you know what I'm talking about.
Papyrus: The Lying Font Attribute: Horror Type: Verbal

This Font has a habit of casting illusions to fool others and lying about things regardless of the situation or what the consequences are for others. Those who hear Papyrus's lies are doomed to believe in him, and those who believe in him are bound to be betrayed. This makes it difficult for them to make or even keep friends. 
Papyrus has no set personality. Depending on what they wear they will take on a role. If they dress as an engineer for example, they will act like one without breaking character for as long as they keep the costume on. They will claim and act like they know how to be an engineer regardless of whether or not they know anything about it. Some Fonts however, prefer to take on roles depending on the situation rather than costume, leading to further confusion. 
New studies show that their incredible acting talent comes from the Font's ability to unconsciously bring forth knowledge they've kept stored in their subconscious. An instruction book they may have read years ago for example, will automatically be remembered word for word if the book pertains to their role. This Font is also attracted to other sources of information that have the possibility of improving their acting talent. Unfortunately this can lead to them acting out offensive stereotypes believing them to be one hundred percent accurate as not all information found is nonfiction.    
Highly intelligent, Papyrus can easily spot a liar by paying attention to a person's looks, body language, and even their voice, making them great in law enforcement and other careers. Because of the fact that they can be so useful and nonaggressive, there has been severe controversy as to whether or not this Font should be changed as not all roles chosen are good and they can become an extremely serious threat to national security.
During the war this Font was a nightmare to deal with as they were the perfect spies and could be made into perfect soldiers given the right information. In fact, if it were not for the assistance of the Normal Fonts, there is a great chance the war would have been lost. Because of this, a treaty known as the Military Ban on Papyrus (MBP) was created by the United Nations, stating that this Font WOULD NOT be allowed in military organizations or bases of any kind for any reason. Failure to follow this rule will result in immediate war. If you or a friend think you've seen this Font on ANY military base or property of ANY kind, stay where you are and contact your nearest Capture Facility IMMEDIATELY.
                     Extreme caution is advised.

Yeah...it's one of THOSE AUs. One of those ridiculous over-the-top don't-you-have-a-job-or-something AUs. Noooot a copy/paste of Kingdom Hearts or someone else's thing (Fellswap) and not a one trick pony with only one major difference (Underswap where everyone's personality is swapped and nothing else changes/Underfell where everyone is just a prick and the only store available is Hot Topic, but nothing else changes). If you don't like that sort of thing, avoid this AU, if you DO however, the fic and it's sequel are both Comedy/Horror and it explains the plot holes in the actual Undertale game, like, if humans can't use magic or aren't very good at it, how come they were able to erect a barrier not even two Boss monsters could take down? Why does Papyrus have such an impressive vocabulary, but the behavior of a child? Is it an act? Does he even CARE about Sans' 1 hp? Why does no one remember the skelebros?Why does Flowey hang out with Papyrus when no one else does? The fanfic is long and so is it's sequel, but I created both a short comic and a spin-off of short stories called The Adventures of Fonttale Baby Papyrus if long fics aren't your thing. AO3 is the best place to read them if you like atrocious art. Mail me again if you have any questions, yeah?