Monsters are one of the core themes of any work of fantasy. Whether it's literature, film, or even video games, anything in the realm of fantasy generally includes some sort of monster or creature that isn't seen on Earth. Sometimes they're based on folklore, sometimes they're the artist's own unique creations, but either way, they're always pretty memorable.
Fantasy cinema has seen a lot of monsters come and go, which have only gotten better and better with the advancement of film technology. These aren't exclusive to high fantasy either--some of them are equally present in low fantasy and dark fantasy. Whatever the subgenre, whatever the target audience, these are the greatest monsters in fantasy movies, which have earned their titles due to their creativity and memorability.