Board Thread:Questions and Answers/@comment-27411407-20151216215702/@comment-26123021-20151229121321

The tipping point isn't NEO- it's the last random encounter of Hotland/CORE. Mettaton NEO in a Genocide run (he still appears on a neutral as long as Undyne the Undying is killed, I think) cannot be spared. Well, the neutral NEO can't be spared either but you get what I mean. Once you make the decision to spare or kill, that's it.