When Mechagodzilla fires its chest beam at Rodan, he lands on his back, but when Baby Godzilla calls out to him when Mechagodzilla is killing Godzilla, he is on his belly.
When Rodan flies over the sea, it creates a parallel series of shock waves on the surface of the water. There are flashes under the water that reveal that the shock waves are actually created by explosive charges under the water.