Grim Tales: Rebirth is a story taking place in the same universe as the webcomic Grim Tales. Rebirth tells tales of other characters in the Underworld that don't appear in the comic. The stories may span from before the comic to the present of the comic.
The first story in Grim Tales: Rebirth. It centers around Inferno McLain, the son of Ember McLain and Skulker, who goes out of the Ghost Zone and embarks on an adventure.
A story about the Underworld in a previous state and how the new Underworld came into existence. It follows the 'Papyrus Ending' of Undertale in which only Sans and Papyrus are alive.