Board Thread:Questions and Answers/@comment-27824864-20160305202956/@comment-26426764-20160305203919

It's not quite known yet which is which, but I believe Napstablook is Asriel- and by extent Flowey- and Mettaton is Chara.

Muffet and Grillby, along with characters like Temmie, Monster Kid, Bratty and Catty, etc. Don't get changed, they aren't important enough.