Ya dun goofed mike

If you are wondering why Mettaton is here, he wanted to try his talents in the horror genre. No one told him that Mike might try to alter his difficulty which would require him to tap into his mainframe. Mike, never having seen advanced robotics like Mettaton's, set him to Mettaton NEO on accident. So anger over being messed with and the program telling him to kill humans culminated into a very, bad time.

Fnaf Copyright Scott Cawthon
Undertale Copyright Toby Fox