Whether new or old, the role of a monster is to be scary. Right?
Does it turn invisible and hunt it’s prey like a certain alien race in a series of movies most of us know? Does it have sharp teeth that can tear through steel? Can it manipulate your mind into seeing things that aren’t there while it devours your soul?
When creating a monster, I try and give it at least three scary features. I usually start with their appearance. Once I have that detailed I’ll give it a couple of deadly weapons or abilities. Then if it’s still not scary or at least dangerous enough I add speed, strength, size, vision, sound or some piece of natural instinct or lifestyle to the mix. By the end of it, you should have a monster that is frightening and deadly.
Of course, there are plenty of things you could add that I either didn’t mention or I don’t add myself. But… the main thing to remember while creating anything, is to have some fun!