Who are the hidden monsters in Godzilla: KOTM?

seeing as we are getting a flashback scene to 2014 (you can actually see that in the trailer), it is highly likely that we are getting to see the Muto's again.

Kong will most likely be teased in the end credit scene, but that might just be a mention and not a full look of him.

I'd like to see the MUTOs get a name

^

Seeing as the name for all monsters has been changed from Muto to Titans, I think the Mutos can keep their current name seeing as they are the only ones to get that name.

Personally, I think we might get a couple of new monsters.

KaijuWorld, I thought that looked like the San Francisco battle. I’m curious storywise what a flashback from that battle will be used for.

I wouldn’t mind seeing a lower power level Godzilla monster being used as a quick cameo similar to Kamoebas in Tokyo SOS. I’d be excited to see some brand new kaiju as well.

Probably some throwaway monsters for Godzilla(Or the other three) to kill.

Cinema blend just posted something about anguirus and biollante being the 2 other monsters. But it doesn't say anything about a source . ???????????????

Bagan confirmed.

Now Gman, you stop that you rascal. 

Bagan should be MonsterVerse's Thanos.

"In time, you will know what's like to finally appear in a Godzilla movie"

-Bagan.

Supposedly at the end there are supposed to be several monsters bowing to Godzilla, including a giant Wooly Mammoth. Don't have the source for that but read it elsewhere and doesn't sound too far-fetched.