Season 3 (Prequel)
From Glitchtale Wiki
Glitchtale's Season 3 (Prequel) occurs in the same world, but is situated 1,000 years before the present. It will elaborate, in dynamic detail, the events leading up to the War of Humans and Monsters mentioned at the beginning of Undertale.
Prequel Shorts - Glitchtale Origins
Glitchtale Origins: The Black Beast
Glitchtale Origins: Kanashi Fukitsu
Glitchtale Origins: Kody Fallenfire
Glitchtale Origins: Gaster