11 Most Terrifying Sci-Fi Movie Monsters

11. Assimilating Alien - The Thing

The Thing from, um, The Thing, might not be the most subtle creature on this list, but that doesn't make it any less horrifying. In fact, it's transparent visibility in the film's mind-melting gore and creature effects sequences (some of the best ever committed to celluloid) just make it all the scarier and more memorable.

An alien of ambiguous origin buried in the Antarctic ice for some 100,000 years, the Thing has the ability to infect, absorb, and mimic any living thing in comes into contact with. What's more, this mimicry is perfect, and even the person affected might not even realize what's happening. Furthermore, each individual cell of the alien is its own separate entity, meaning if it entered into a dense population, it would infect the entire world in a matter of only weeks.

If threatened, the creature has the ability to contort and mutate itself into horrifying abominations on the fly to protect itself, individual limbs and body parts sprouting eyes and legs and tendrils to escape harm. If all else fails, the various "things" can meld together into a single, giant mass fleshy mass of tentacles and deformed human features.