I think the title says enough

undertale yellow AU with fucking swearing and violence and death and shit, so if you don't like that, too fucking bad

Moray, beloved member of the Feisty Five, gets ill without reason and ends up ultimately falling down. Ceroba, dear friend of the posse's leader, gives them a PSA from the Royal Lab, who could find a way to save them. But what is about to unfold is a lot more ghastly than what they could ever imagine.