Made in Abyss: Official Anthology is a compendium of short comics set in the same world and with the same characters from Made in Abyss.
It's a parallel series from the same publisher, Takeshobo, and with Akihito Tsukushi's blessing, that gathers the work of multiple guest professional artists to tell non-canon stories, with some of them being serious, while others are totally silly or humorous.
It has been published on Webcomic Gamma, alongside with Made in Abyss, since 2017.