
If we're going by MonsterVerse creatures, then Titanus Leviathan or Kraken. But if I could manage it, I'd probably slip Anguirus or Baragon or Varan in there somehow.
A true fan can acknowledge the bad while still appreciating and cherishing the good.

And how exactly would Gigan fit into the story?
A true fan can acknowledge the bad while still appreciating and cherishing the good.

^
I would go for Mokele-mbembe
Zwei Wing is the best singing duo. Change my mind.

Gigan would be awesome... so would Destoroyah... and Biollante... They'd all fit really well. But I have to go with
Keizer Ghidorah
... or Desghidorah
Imagine what having other Ghidorahs could mean! It'd mean there could be a whole planet of them! A whole herarchy! It could mean a whole war between the Earth Titans and the Ghidorahs, or against a single, extremely powerful version of Ghidorah!
If people weren't lazy, we wouldn't try to be efficient. If we weren't efficient, we'd never get anything done.

TheLazyFish Or how about a war between different species of Ghidorahs?
A true fan can acknowledge the bad while still appreciating and cherishing the good.

Monster X/Keizer Ghidorah was going to be my first answer but Gigan would be great if they introduce advanced alien civilizations. Essentially being a more advanced rendition of Mechagodzilla, being complete cybernetic with both synthetic and organic parts harmoniously blended together

That'd be ****ing amazing!
If people weren't lazy, we wouldn't try to be efficient. If we weren't efficient, we'd never get anything done.

Q : Titanus Qetzalcoatl.
Y'all know that old movie at least needs a "Q2".
Ooh, one more, Titanus Tetanus. Ouch!
~Rift Rat.

I'd probably put in Anguirus. Since he seemed to be teased in Godzilla's undersea lair, I would theorize that there was, in fact, a monsterverse Anguirus, but there is one thing wrong with this theory: How did he die? Did he die many years ago? And to who, or what did he die to? Anyhoo, I would expect that he would have the same symbiotic relationship that Godzilla has with Mothra in KOTM.