The original Boris Karloff "Frankenstein" has always been my number one monster movie. The book was good too but different from the movie and both brought chills to me as a kid. Another "monster" was the lurker in Bradbury's "Dandelion Wine" a subtle yet terrifying evil. And, of course, "Freaks" the 1930s movie has sent chills down my spine every time I saw it. There are other, human monsters, such as the evil in Bertolucci's "1900" and the Nazis in "The Tin Drum." Not all monsters come from outer space. I think your monster creatures are great (but they need more shadow and dark in the illustration) Thanks.
About a year ago I put some fantasy sculptures in a store window and was called to take them out when a little girl was scared of one of the figures, a clown. It puzzled me a bit, but it seems that kids, some of them anyway, are scared of clowns. So the clown picture certainly touched base with me. The other images are amazing.