What I believe the origin stories for Rodan, Mothra, and King Ghidorah could be in the Legendary series

This seems to go pretty closely with other theories. The ones up for debate are Ghidorah, and Mothra really everyone expects Rodan to basically share Godzilla's backstory.

I hadn't actually considered the idea of Mothra being from the Carboniferous, but it makes sense. Toho used the same origin for the Meganula and Megaguirus, and it could easily work for Legendary's version of Mothra.

As for King Ghidorah, I also like the idea that the meteor that killed the dinosaurs at the end of the Cretaceous acted like a sort of cocoon or egg for him, and that he remained dormant for millions of years, until recent changes to the planet have allowed him to emerge and wreak havoc.

And I agree with pretty much everyone else that Rodan should just be another creature that evolved alongside Godzilla. 

Don't know if its considered canon, but in the novelization of the 2014 movie, Mothra is hinted to be Ford's pet moth, who apparently hatched from her cococoon after the nuclear meltdown

Don't know if its considered canon, but in the novelization of the 2014 movie, Mothra is hinted to be Ford's pet moth, who apparently hatched from her cococoon after the nuclear meltdown

Don't know if its considered canon, but in the novelization of the 2014 movie, Mothra is hinted to be Ford's pet moth, who apparently hatched from her cococoon after the nuclear meltdown

Don't know if its considered canon, but in the novelization of the 2014 movie, Mothra is hinted to be Ford's pet moth, who apparently hatched from her cococoon after the nuclear meltdown

Mothra will not be the cocoon at Janjira. That was just an Easter egg referencing Mothra. Making Mothra somehow a mutated moth that grew to kaiju size is not only unrealistic by Legendary's standards, but it completely spits in the face of the character's entire legacy. Mothra will be some sort of ancient creature in Godzilla 2, possibly with a mysterious past and some sort of vague mystical element that causes some people to see her as a goddess.

They all seem reasonable enough...well done!

I like how they fit with the realism of Legendary's Godzilla.

Polycephaly of more than two heads is something that's nearly impollible to exist in nature, and i also don't think that they are going to introduce an alien, when they have monsters. I think that King Ghidorah is going to be the result of MONARCH, experimenting with MUTO DNA. They are confronted with something dangerously new (Godzilla) and since atomic weapons doesn't work, the first thing to do is to create another weapon against the threat!

Rhodan and Mothra are going to be ancient creatures. So it's more likely that the world is going to work on a weapon that actually works.

Problem, Destoroyahx. Modern-day genetic engineering is nowhere near that advanced as to create a new life form from the DNA of existing animals, even giant monsters like the M.U.T.O.s. There is no truly logical way to really do King Ghidorah without suspending disbelief. But at least with the extraterrestrial origin, although it can be considered a cop-out handwave, has the benefit of the rest of the universe being the reason for his existence.

I think making King Ghidorah an extraterrestrial is the best way to make him plausible in Legendary's series, plus it's the most consistent with his most popular origin. If King Ghidorah were just a creature that came from somewhere else in the universe, then it leaves a lot to the imagination. A lifeform like that would probably never evolve on Earth, while there's no way that humanity would be stupid enough to create him, plus making him genetically engineered would push the boundaries of realism more than making him an alien.

The thing is, we don't even know what types of lifeforms exist out in the universe. For all we know, a creature like King Ghidorah could be out there. Legendary exploited the fact that humanity knows so little about what lies deep under Earth's oceans to justify Godzilla's existence, and they could do the same with outer space for King Ghidorah. They don't need to explain where exactly King Ghidorah came from, why he exists, or exactly how he got here. All that matters is that he has arrived on Earth, and poses a serious threat. That same approach has been used in some of the greatest science-fiction films in order to introduce an extraterrestrial lifeform while still remaining grounded. In a universe where giant monsters from the Permian are roaming the Earth, a giant three-headed dragon coming from outer space isn't that much more of a stretch.

You know I've actually been thinking about making some fan made origin stories for some of the other monsters from the Godzilla series would you like to see me do that?

Now normally I just ignore the whole topic when someone says ghidorah will come from space but this one makes more sense. Mabey when Ghidorah is in his egg the outside everment doesn’t affect him kind of like how a seed works. It can be dormant for 100s of years but can just start growing (or in this case be born) whenever it feels like it or when the outside everment is right for it. But still it is more likely ghidorah will originate on earth because it is far more believable but you're isn’t too far of a stretch. 

ULTRAZERO80 - These are exceptionally neat concepts you have presented! I especially enjoy the thought you have placed into the origins of Ghidorah and Mothra! Personally, I believe Ghidorah arriving via space is perfectly fine; our galaxy is vast, and the universe surrounding it is even larger! There is no telling what could be out there amidst those countless trillions of stars - or what might one day find us. Thank you ever so much for sharing these concepts with us! :)