That is Nightfall. He's an Errormare child.

That is his cape.

And that is his soul.

Name : Nightfall

Age : He's twelve

Mother : Nightmare

Father : Error

Friends : Gradient, Horror, Killer, Dust, Cross, Core Frisk, Fresh, Geno, Blue

Other relationships : Dislikes Ink, doesn't know much about his uncle Dream

Likes : His favourite colour is red, he likes writing random stories

Dislikes : Other being afraid of him, HATES bullying

Since he doesn't like it when others are afraid of him, he wears a cape to cover his tentacles and gloves to hide his hands. He can change his eyelights, so they'll look similiar to uncorrupted Nightmares eyes.