71% of Earth is covered with water and many parts of the oceans are still unexplored by mankind and researchers believe that there are a lot species waiting to be discovered. The lack of ability of humans to breath underwater is one of the biggest barriers to explore the deep but also the encounters of monsters living down there will be the most terrifying encounter you will experience.
One good example is the monk fish also known as sea devils, most found in the coasts of Europe. Just by its nickname, you can see how scary it is and it looks like it comes from a different planet. They are predator in the deep with enormous jaws enabling them to swallow their prey in whole and fully as large as itself.
The monkfish on the video is found 80 miles off Gibraltar and noticed how the monk fish stares the camera.