What do Ysgardians fear?

[Akai]

OK, to answer the question, what do I think residents of Ysgard in general, not adventurers, are or ought to be afraid of:

They ought to be afraid of things that have hurt them in the past, of things they have been taught to fear, or that they can see for themselves are dangerous and likely to hurt them a lot. They might fear death in the same way that we fear traffic accidents: If they happen, you'll suffer considerable pain, lose a substantial bit of property, suffer serious inconvenience, and though the odds are good that you won't be permanently killed, it happens frequently enough that everyone knows someone who knows someone who didn't come back.

Every resident would react to their fear in ways varying with individual courage and individual training/practice in facing fear, along with (if they are religious) the knowledge that the Aesir expect them to show bravery.

[AmusedApathy]

Poor Legs is scared that she'll someday have to come up with a reason to actually like the stale candy in Bastion, that harm that she can't stop will come to Dan'eth, and bridges! That's plenty of phobia's!! (And a really good excuse for her imported candy stashes say maybe under Lexy's couch, or under the cushins by Rali's house, and a couple of others that are super sekret candy stashes!)

[Michiko]

Theruvial's only fear is to be a failure to her friends and faith. Not that she cares what most people think but some specific individuals have opened her eyes and she fears that actions on her part could bring disgrace to them.