IF YOU KILL TORIEL, UNDYNE, AND PAPYRUS, YOU GET A METTATON ENDING. IN A PHONECALL WITH SANS, METTATON INTERRUPTS AND STARTS TALKING ABOUT HOW HE TURNED THE UNDERGROUND INTO A SHRINE TO HIM, AS HE IS NOW KING. HE MENTIONS HOW HE WASN'T THE NICEST TO ALPHYS AND WENT TO APOLOGIZE. HE THEN MENTIONS THAT HE COULDN'T FIND HER ANYWHERE.
BUT, IF YOU KILL TORIEL, UNDYNE, AND PAPYRUS, ALPHYS KILLS HERSELF. SO METTATON DOESN'T KNOW AND STILL THINKS SHE'S ALIVE. OK HERE WE GO: