Something I've discovered here at AFF -- no matter how weird or dark I get, there is somebody much wierder or darker than me.
I personally don't get the tentacles fetish...Seriously. It boggles my mind that it is actually a bonafide story code.
The most nonhuman I've gotten in my fan fics is describing graphic sex with Nightcrawler making use of his tail and an array of "attachments" for the disfigured Cyborg from Teen Titans.
Oops...Almost forgot I posted some of my Gargoyles fics on AFF.
They're pretty anthropomorphic though. At least some of the Gargoyles (from the Disney animated series) are definitely hot. All that rock hard muscle running around in loin cloths... Goliath has that deep rumbling voice.... And they can swoop you up and glide away into the night...The females are pretty good looking too and don't wear much more.
I might be interested in reading or someday writing about spirits or other creatures that aren't bound by the usual physical boundaries of sex. That could be interesting. Anne Rice did a bit of that in her books. But, that's about it for me.