Films: Leviathan (1989)
Location: Haunted home/Ocean
Height/Weight: That of an average human.
Summary: Somewhere in the briny depths, pure terror comes in droves. And we've seen it before. Now, prepare to be boxed in with an oceanic mistake of human science...
History: Somewhere in the deep sea, a Soviet shipwreck known as the Leviathan holds a dark secret. All of the original crew were killed when they tried testing out illegal experimentation on themselves, forcing them to scuttle the ship. Unfortunately, the local explorers drank some vodka from there, and now the organism that was created has full access to a bunch of human hosts to evolve within.
Notable Kills: Almost everyone infected by this thing becomes a part of it. On the outside.
Final Fate: After the beast achieves a monstrous final form, it is seemingly killed when its crushed by the lift of the exploding base. Then it appears again just to have a lit demo charge thrown into its mouth, killing it.
Powers/Abilities: Can absorb its host's genetic code and body into something more threatening and big.
Weakness: Anything conventional.
Scariness Factor: 4-It's not seen very often, but this thing is what happens when body-snatchers just drop all subtlety and literally start wearing their handiwork on their sleeve. Its final form looks like a horrible mish-mash of humans and deep-sea fish, and it's pretty tricky to kill too.
Trivia: -There were over fifty different ideas for what the creature would look like, and in the end, the final design combined elements from just about all of them.
-If you can believe it, they almost had chicken feathers in the underwater sequences to give off the illusion of actors actually being in moving water. It fell through when the feathers moved side-to-side instead of up-and-down.