I really love the movie The Mysterians, an early 50's flick from Toho about aliens who invade the Earth to breed with our women. It's a great lark of a sci-fi outing which landed amongst the monsters before Toho gave over to Godzilla and his kin. Invasion of Astro-Monster is The Mysterians with Godzilla and gang, and it's a lot of fun. If features an American co-star, Nick Adams, present for the sole reason to make the movie marketable overseas. And he's an enthusiastic addition to Toho stock company of seasoned pros.
But focusing on Godzilla himself for a moment let's all agree that the movies never got sillier than one single moment in this highly memorable screen saga. The aliens (called "Xillians") are attempting to trick mankind into thinking their invasion is not that and that they mean us only the best, such as when they offer up a cure for cancer. They say they are afflicted by King Ghidorah on their homeworld "Planet X" out around Jupiter. But they are liars and Ghidorah is under their control and by trickery theyget Godzilla and Rodan also who fight off Ghidorah. As he flies into space Godzilla crosses his arms and jumps for joy in a move called a "Shie dance" after a cartoon character who performs the move and yells "Shie". It's goofy and lots of folks including the director didn't like it, but it stayed and after that Godzilla moved into another place completely.
Like most hardcore Godzilla fans I hated it for a long time, but I've changed my mind and embrace it. Godzilla in this movie is not the "Big G" of other films, he's a movie star who can appear in a range of different kinds of movies and comedy is just one. More next time.