NIGHTcrash!sans [NOT A SHIP CHILD]
Story: As ERRORcrash sans was experimenting with code, he fused some of nightmare's sans code, to see if it could make him stronger. but the clone desoved as melted. this was seen as a failure, and ERRORcrash sans disposed of the clone. unknown to him, the clone code had fused with the nightmare code. this clone wanting more power went on a rampage threw many au's to gather negative feelings, and to become the strongest anomaly in the multiverse. But Nightmare sans responded and captured the clone, to use him as a deadly option, and last resort. The clone now locked up, feed off the negative feeling from those trapped with him. The clone dubbed himself NIGHTcrash!sans.
CREDIT ERRORcrash sans by errorcrashsans
Nightmare sans by JOKU
UNDERTALE by TOBY FOX and origanal designs be TEMMI CHANG