Necromancy, demoncraft, black arts, those are all magic crafts that are, by and large, really accepted nowhere. xD Except Zantaric. In Zantaric, people are free to practice the dark arts all they want. Everywhere else, they would have to be pretty secretive about it. I'm sure there are plenty of underground cults (likely some large ones, too) operating in the big nations.
It's loosely accepted in Thanatos. Necromancy is a pretty big classification and mediums, people who can commune with the dead and spirits and such, technically falls under necromancy, and Thanatos is aaaall about their mediums! So necromancy isn't a black and white thing. However, Thanati don't classify their mediums as necromancers. Necromancy is also something that runs strong in Thanati blood in general, but they still don't allow things like body-raising and zombie-making and such, and would view that as illegal and vile. Plus, Thanati were originally driven off the mainland because the other groups in Le'raana persecuted them because they associated them with body-raising and zombie-making.
Thanatos has a number of underground cults that delve deeper into necromancy, though.
For individual characters? They're free to see necromancy as a divine art! While most cultures in SotE view it very stereotypically and negatively, individual characters can view and practice it based on their own beliefs. They just probably wouldn't want to be open about their practices because most people will hear "necromancy" and think "evil!"
As for Fell,
@Kalak has the right of it!
As for culture and such, that's all unknown! And is pretty much supposed to remain a big mystery. It was a long, long time ago that all that happened--like the equivalent of us trying to make sense of a city that we just unearthed and didn't even know existed. That's what Fell is. Characters can totally find artifacts and have theories about what Fell was like before its fall--after all, Serenians and Connlaothians are spin-offs of the place. But there's nothing definitive, and it's been so long that there are many, many generations between then and now and thousands of years of history. A lot has been lost to time.
As for adding races to the wiki--I'm actually currently working on a system for adding species and races and such to the lore! 8D I'm not sure how much longer it will be before it's fine-tuned and finished, but feel free to write up your races in the meantime. <3
