Post /x/-tier anime/manga/etc..
Umineko is pretty /x/-tier if you ask me.
Mushishi - Spirits
Evangelion - Kabbalah
Fullmetal Alchemist - Alchemy
Ghost Stories -Ghosts
Serial Experiments Lain - Too much to mention
Mononoke - Spooky stuff
Steins; Gate - Time Travel
Haibane Renmei - Angels
Angels Egg - Eggs and Angels
Musaigen no Phantom World
Natsume's Book of Friends
Please watch this, there isn't a proper ending in the anime, but this seriously is precious and lovely and it filled a lot of good hours.
Gregory Horror Show is definitely /x/ material.