Don't Go In The House and Jacob's Ladder when I was about 5 or 6 years old. Parenting failure.
Both absolutely fucked me up as a kid.
Unsolved Mysteries, IT, and Communion as well.
I straight up had a fear of the dark that lasted a long, long time, and I don't just mean as a kid. That's how badly I was scarred by those movies. It didn't stop there since I was a horror fan from that point on and would watch anything, my parents didn't seem to give a fuck what I watched.
Don't Go In The House had *full* frontal nudity, and not for some sex scene, but the woman getting torched alive as she screams and begs. Great viewing material for any 5 year old!
Jacob's Ladder to this day freaks me out, I wouldn't be comfortable watching it alone at night, and same with Communion.
It's funny, I never knew until I finally found the movie again like 2 decades later that it was a very silly comedy but I will say Killer Klowns from Outer Space scared the fuck out of me as a kid thanks to the clowns themselves. They definitely looked creepy.
Psycho 2 deserved an honorable mention for the creepy mother voice and various scenes in the movie with the silhouette of the mother character. The ending used to creep me the fuck out.