Season 3 (Prequel)

From Glitchtale Wiki

Season 3 of Glitchtale (more commonly referred to as The 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 in the beginning of Undertale.

Prequel Shorts - Glitchtale Origins