Board Thread:Questions and Answers/@comment-26242189-20160401075054/@comment-34266327-20180413154648

If you don't date Papyrus, (Or Undyne and Alphys who can be dated If you date Papyrus.) you will probably get a neutral ending with Sans asking If you are scared to fight or something (I don't know If this neutral ending exists or not.)

If you do date them, you will get the true pacifist but with some differences maybe.