Recommend me some crazy MC :) Like, a killer? I'm looking for horror-ish. Hmm...strong and...

Here are some MCs that range from a bit off to completely bonkers
http://www.mangago.zone/read-manga/wolf_mary/
http://www.mangago.zone/read-manga/prison_lab/
http://www.mangago.zone/read-manga/rikudou/
http://www.mangago.zone/read-manga/ludwig_revolution/
http://www.mangago.zone/read-manga/toumei_ningen_no_tsukurikata/bt/338417/Vol1_Ch1/
http://www.mangago.zone/read-manga/kami_sama_ki_sama_o_koroshitai/

the_moon_is_beautiful_tonight_but_first_die

*cough* http://www.mangago.zone/read-manga/the_moon_is_beautiful_tonight_but_first_die/

Strong and smart, mentally fucked :

Warehouse http://www.mangago.zone/read-manga/warehouse/

http://www.mangago.zone/read-manga/monster/