Board Thread:General Discussion v2.0/@comment-26347196-20151109173852/@comment-5956954-20160107002612

IMHE, undyne the undying is harder than sans. sans has this, new shock type of value, so his attacks will seem impossible until after playing against him a ton of times, so then, while his attacks are quick and powerful, they have an easy to learn pattern.

Undyne the Undying on the other hand, while she does have patterns on her green soul attacks, there are many red soul attacks which require alot of concentration, planning and quick thinking. for example, the spears that surround you and the ones thrown at you and sometimes, the slow arrows in the green attacks. they favor RNG instead of a fixed hard to avoid pattern, so it will be different each time and can get confusing.

again, just my experience. i beat her by luck in 4 tries, but when i vsed her again, it took me 12. sans took me 13, and other times, barely 3 or even just 1 try.