Possibly the most underrated fanfic from the Undertale library, Alphys' Adventures is a simple yet funny and charming fic written by xandermartin98 that revolves around Alphys, Undyne and the skelebros teaming up and exiting the underground together on a surprisingly action-packed and hilarious journey to stop Mettaton from taking over the entire world with the sheer weight of his immense popularity. The story is also quite lengthy for what it is, clocking in at about 25,000 words divided into 13 chapters.