what kind of dysphoria do fictionkin tend to feel in general?

Depends on the kin in question. Here’s what I can tell you.

Surveys show that the overwhelming majority of kin (who answered the poll anyway) are transgender of some stripe. Something like 80-90% of us, running the spectrum from ftm and mtf, through genderqueer and nonbinary and others. So a lot of kin feel gender dysphoria, probably do to a mis match between their current gender, and the gender of their kinself.

Some kin also have difficulty when they look in the mirror, sometimes expecting to see the face of their kinself.

Non-human kin especially have confused feelings about their bodies. They often miss, or can still feel sensations from, limbs and features that are entirely missing from their human body. (wings, tails, horns, etc).