Horror

http://www.mangago.me/read-manga/kami_sama_ki_sama_o_koroshitai/
Feeding Lamb is pretty dark, I recommend that if you haven't already read it

http://www.mangago.me/read-manga/sweet_home/

Bastard

http://www.mangago.me/read-manga/bastard_hwang_youngchan/

Best horror psychological I've ever read

http://www.mangago.me/read-manga/pumpkin_night/

if you have the line app go read melvinas therapy like its the best horror manhwa for me amazing story and hidden secrets in every chp and the author explains everything which is great

+100

http://www.mangago.me/read-manga/emerging/
http://www.mangago.me/read-manga/manhole/
http://www.mangago.me/read-manga/uzumaki/

http://www.mangago.me/read-manga/ibitsu/

http://www.mangago.me/read-manga/chiller/

http://www.mangago.me/read-manga/ichi_the_killer/

http://www.mangago.me/read-manga/doctor_du_ming/

one shots:
http://www.mangago.me/read-manga/layers_of_fear/
http://www.mangago.me/read-manga/hell_baby/
http://www.mangago.me/read-manga/human_chair/
http://www.mangago.me/read-manga/bradherley_no_basha/