Board Thread:General Discussion/@comment-37345491-20190406164451/@comment-39394247-20190604185040

User1204: "If you take Undyne out of the game, you have no challenge during genocide whatsoever, and while it does make genocide boring, it also makes people with a lot of time on their hands more curious, and with no challenge at all, they'll ruin their true pacifist route"

Sans is quite a challenge on genocide, however there's no challenge for the Alphys ending if you remove Undyne. However, I think Sans is overrated.