

Manda could also exist if the MonsterVerse followed the laws of physics.
“Banana oil.”- George Takei, Gigantis: The Fire Monster

Realistically, giant monsters don't and can't exist. Literally any relatively-well-versed giant monster fan knows this.
That's not what Legendary is doing with the Monsterverse. They're taking a "grounded" approach, trying to figure what kinds of roles in the global ecology giant monsters would play, like real-life animals. Godzilla is an apex predator, top of the food chain, whom deals with competition such as Shinomuras and M.U.T.O. parasites.
Basically, figure out a grounded design for an animal on Earth that would benefit it as a competing organism in the global ecology. For example, Anguirus is a logical design, a large and heavily armored quadruped that is suited for burrowing and slow, rhythmic "dance-like" combat.
Honestly, out of the current Monsterverse, only creatures like Shinomura and King Ghidorah are a bit out there.

Varan could possibly work if he has similar wings to the M.U.T.O and possibly titanosaurus.

Gezora: A prehistoric Squid that inspires the Kraken stuff
Baragon: Prehistoric Reptile
Anguirus: Evolved Ankylosaurus
Zilla: A theropod that was mistaken as Godzilla by some New Yorkers
Gorosaurus: Evolved Allosaurus
Giant bugs: Basically Giant Bugs
Megaguirus: Ancient Dagonfly
And other monsters that are just oversized animals.
Godzilla Generations was a beautiful game! I loved the fact that there's a laser cannon inside of Dr. Serizawa's eyepatch.

I know the Shinomura isn't 100% canon for some reason, bu I'd like to see them appear in a film. A kaiju that can split into multiple parts is a cool idea.

I would LOVE if the opening sequence to Godzilla 2: King of the Monsters directly animated Godzilla fighting the Shinomura, making Awakening 100% canonical and not in a "some elements are pulled but the entire thing isn't explicitly referenced" way, The Legend of Brian.

i think all these Kaiju's develop there own energy fields. they are like bee's, according to laws of aviation bee's cannot fly but yet they do. Kaiju and MUTO's don't care what laws mankind made. they follow there own rules.
YOU.....DUMBBELL!

Actually, that whole "bees can't actually fly according to reality" thing is an urban myth, perpetuated enough that some people actually take it as fact.
Besides, things like "energy fields" and whatnot are more explicit science-fiction, something that the MonsterVerse hasn't been keen on perpetuating as of yet.