Aye, many people are far more scarred by the Beelzebubs than by anything else in the game. They seem to be hands down the most universally feared monster to lose to. And yeah, they are pretty darn gross, but Chrome and Fredrika and the zombies win out over them every time in my book. (god I can't believe I misspelled that the way I did) The Genie also gave me one heck of a jump scare when she revealed her true form. Ilias' war face was also REALLY damn creepy, especially with how sudden it was. But you haven't gotten to Ilias' war face yet. The Chimera Dryad, Chimera Dryad Vore and the Chimera Beast are also pretty freaking nasty just because of how... wrong they look. Most ironically given her namesake, ****n was actually pretty cute, at least in disguised form.
Oh my gosh, you haven't fought Imp yet! My god, Imp is the HARDEST MONSTER EVER. Seriously, she will destroy you with extreme prejudice and there is NOTHING YOU CAN DO TO STOP HER! [/sarcasm to the max]
Edit: I keep forgetting that appearantly the term in astericks is appearantly a racial slur, even when used to describe one of Lovecraft's Eldritch Abominations.