I really love the description on IMDB:
So this film concerns hooded aliens who come to Earth with plans to capture and have sex with Earth women. So they release a huge bird-like robot named Mogera (it later returned renovated in Godzilla vs. Space Godzilla) to prove they mean buisness. The army manages to defeat it by booby trapping the bridge and blowing it up while the monster is using it. Then the battle for the cosmos begins with the Mysterians and their ray firing ships and the humans and their markalite lasers.
Hooded aliens who want sex with our women!! OMG! Keep them away from our women!! 😀
I really love this American trailer:
In case you want to watch the (more superior but less funny) Japanese trailer: