Toho kicked around a lot of strange ideas for Godzilla movies that were ultimately never used, but this one is probably the weirdest of them all. "Bride of Godzilla?" is a completely insane story concept from 1955 that would have involved the King of the Monsters in a subterranean lost world, filled with monsters, prehistoric animals, and even mermaids!
Godzilla and Anguirus would have appeared, along with a giant archaeopteryx and chameleon (possibly precursors for Rodan and Varan, respectively) as well as a mammoth and sea serpent.
The mermaids help out the heroes of the story; as a way of saying thanks the humans shoot one of their babies in the head.
The protagonist of the film is a scientist who made himself a robot daughter; his ultimate creation, however, is a huge robot woman designed as an amalgamation of said daughter and a woman who dumped him (kind of a sicko, huh?). The robo-gal clobbers all the monsters before Godzilla himself falls in love with her, carries her off to his underground lair, and cuddles up with her, not knowing that she's rigged to explode...
As completely crazy as this story sounds, I still think it's a blast. Would it have worked as a film? Who knows, but as a psychotic piece of storytelling that even the looniest fan-fiction couldn't top, it's hilariously entertaining.