This is Nega!Dreamtale Nightmare, also known as Negamare for short. Essentially in this au, the events of Dreamtale take place but the au is more Negatale-esq with Nightmare taking on a Negatale Sans like personality. Nightmare has severe depression issues and ends up eating the black apple which makes it even worse, the human (corrupted) now taking on a voice in Nightmares head, telling him terrible things to make him feel bad so he'll snap. Whenever Nightmare becomes too stressed he explodes with anger, becoming his corrupted state, resulting in him rampaging in a fit of rage, attacking everyone and everything in sight. Nightmare often hops au to au to run from what he's done but always blows up and ends up destroying the au's. Nightmare spends more time in his corrupted form now than his normal one but when he is in normal form he is depressed and when he's alone he often cries because he hates himself, both because of what he's become and what he's done, but he cannot help it.