the mutos

That's actually a good speculation

i would consider this for the movie

You know, the plot of this movie does say something about human's arrogance of creating creatures so you might have somethin correct right there

you might be right dragonlord tevin and yes kaijudino this a good theory, that might be the plot of the movie

I don't know if anyone's found these yet, but when you type in "door to hell" in the mutos database, it says some EXCITING stuff! Type it in yourself, but it says, "GAS RESERVES HOLDING. FIRE MEMBER OBSCURING MEMBRANE LAYER AND FUELING INCUBATION." 

*fanboy squeal*

I think that there might be some new "natural" kaiju as well as the genetically manipulated ones, because this message points to a few things. 

1. this thing is inside a membrane, still in incubation, a scientist could not have constructed a membrane under an eternally-burning hole in the ground, which means it may be as natural as kaiju get. I mean, it even sounds like the "door to hell" might be some part of its SPECIES lifecycle, rather than just a natural gas fire, considering it's growing beneath it, DUE to the flames! 

2. There may be other phenomena that could be expained through these "natural" kaiju, such as the bermuda triangle being a monster that generates massive electromagetic fields. 

3. Godzilla could have temporary allies, or even more enemies, perhaps the natural kaiju would be kept for a possible sequel?

I dunno, I found it and wondered if anyone knew about it or if I were the first one, do with this new info as you will! 

:D