you staged a genocide in the dungeon, ruthlessly killing all the monsters. And now, you have already left the Core and were ready to go to the castle and kill the king, as when you enter the last room of the Core before leaving, you see... Mettaton. Mettaton at its strongest form is NEO. Mettaton grins at you, and then speaks arrogantly. Disgust for you can be heard in his voice.

WELL-WELL... HELLO, DARLING. READY FOR YOUR DEATH, HUH? ALTHOUGH... I DON'T CARE... YOU WILL DIE!!~