Board Thread:General Discussion/@comment-26347196-20160410032827/@comment-4560646-20160526005738

Took me 6 tries to defeat Undyne the Undying. She's hard. Took me 3 tries to defeat Sans. He's easy. All you have to do is throw the Real Knife into a dumpster like the useless piece of trash it is and get the Burnt Pan instead, then have your inventory contain Butterscotch Pie, Instant Noodles, Steak in the Shape of Mettaton's Face, three Snowman Pieces or Legendary Heroes, and Sea Tea. Then practice, practice, practice. Unlike Undying, Sans' attacks are not randomized, after enough trying you'll learn his patterns. You have the edge on his boss fight.

Of course, there's the fact that I'm good at platformer games and have no experience with the Dance Dance Revolution series.