I have a few things to add to this list! (Mainly because I'm afraid of everything!)
First of all, in Super Mario RPG when you get up to Smithy:
Look at that backdrop. The whole thing is a battlefield made of the heads of the bad guy. Well, uh. His head is transforming in this picture. But all those red things are a bunch of his heads staring at you. Into your soul. Judging you
for not being able to beat Culex. Next, in Postal II...Cats. If you know anything about Postal, you'd know that you can use cats as silencers. So how would there be anything freaky about the cats in Postal? Well, if you go into the back of the pet shop at the mall. Oh boy, is something waiting for you. All the music stops and you can see cats that have been skinned on the tables. And blood is splattered everywhere.
In fairness, what was I expecting from a game like Postal II?
(I also couldn't find a picture of it. Maaaainly because I don't want to.)
Then in just about every Wario game:Is it just me, or do the Wario games have some FREAKY bosses?
Here, take a gander, tell me if you don't wet yourself. (Lot's o' spoilers ahead!)