Undying is hard

Most of the attacks follow the same pattern every time

Then you try shaky handedly fight her on the switch

*try to

Oh I did
Once you do it seventy eight times, it gets easier
It just takes repitition.

As someone who no hit Undying, Undnye The Undying is easy

Sans on the other hand...

I can't bean sans
Undyne The Undyning is easy