The comments below may contain unmarked spoilers. I don't expect many people will solve it without doing at least some Wikipedia lookups, but you're welcome to try.
At last I solved it! From the perspective of someone who doesn't usually do crosswords: this was quite difficult. I did have to resort to Wikipedia-ing and (in some way worse) Googling for many of them, but it was fun.
ROT13 of my solutions that the website in the original post will accept as input to the "Save/Load" button after decoding:
Just in time for Halloween - the spookiest themed crossword puzzle of the year!
The comments below may contain unmarked spoilers. I don't expect many people will solve it without doing at least some Wikipedia lookups, but you're welcome to try.
Enjoy!