Board Thread:General Discussion/@comment-25983468-20160329120934/@comment-25181180-20160329143238

Undyne seemed to releases her full power during the Undying battle, and have the ability to create her own determination, albeit not as powerful as Frisk or Flowey. If by any case, Undyne knew that Frisk will destroy the Underworld in the Genocide Route, then she should be able to SAVE right before the Undying fight or earlier to stop Frisk, her enemy, earlier; when he just entered the Waterfall, preventing him to collect any armors, weapons, etc.

However, if Flowey and Frisk was perished, then it is sure that Undyne will be the strongest character in the Underworld, if Asgore hasn't absorbed the six souls yet.