Oh no, Undyne is one of the nicest people I know! She just doesn't act like it right away, but she is! She just also has really high standards for people.

[Like, don't be a murderer. Oops, failed step one, Gil.

Continuing to be covered in lion cubs, as they climb up into his lap and over his bones. One even starts tugging at his cape a little, until he starts focusing on them and playing with them instead.]

Yes, to all three! He's good and just and fair, and also kind! He had... a lot of bad things happen to him, but Undyne told me he's never once failed to offer someone a nice hot cup of tea when they go to visit him.