Also, my suggestion is also to have based interests off the Kaiju films from Japan. Not all monsters have to be actually intent on destroying the world or destroying all of humanity. We can even have kaiju that are allied with Earth (not exactly with the humans, but say a common goal so that they can keep their territory in check and keep Earth from going to complete shit). 

That being said, extra-terrestrials can also have a beef with Earth and may even send their own kaiju, cyborgs, robots, and etc to invade as well. I think some of my ideas can also be worked out with Mr. Cold as well, so keep that in mind.