7. Species 8472
They look like a cross between the Animorph’s Hork-Bajir and the classic alien hunter the Predator. So yeah, if he popped up outside of your window, good luck not screaming like a four-year-old on a roller coaster. Beyond that, they’re also super hard to kill. Essentially you’d need a biological weapon to kill these things. Plus they’re from a different part of space. Another universe if you will. That’s just bonkers to think about.
6. The Breen
The Breen are Michael Myers in space. Doubt that statement? They wear a mask you never see them take off. They hardly feel pain, or at the very least show that they’re in it. They don’t communicate conventionally if at all in most cases and they’re fond of the old ultra-violence.
Klingons history has long been established. While an allegory for the Soviet Union, the Klingons are now more Viking than anything. Focused on glory in war, an afterlife with an eternal battle awaiting them as members of the “Black Fleet” (non-canon). The fact that an angry, over-sized, perpetually hangry person with super strength and a desire for wine that has the consistency of blood isn’t scary to some is what’s horrifying.