New Villain purpose in GvK. (SPOILERS)

Godzilla to Kong"You take my life, but I'll take yours too! You'll fire your musket but I'll run you through! So when you're waiting for the next attack, You'd better stand there's no turning back!"

"The Trooper" Iron Maiden, Piece Of Mind,1983

I hope they give him heisei Mechagodzillas theme as his main theme and for showa fans maybe take a page from the book of Godzilla final war and play the showa Mechagodzilla theme in the background subtly like how they subtly played king Ghidorahs original flying sound in Boston just before he arrived on the scene in KOTM.

I think Mechagodzilla is a weapon made to fool the titans. My guess is the Mechagodzilla lures all the titans while posing as Godzilla, making Kong think Godzilla is behind all of this. And when the real Godzilla shows up...FIGHT

Here's my theory: I think that Ghidorah's last head will be involved somehow in Mechagodzilla's creation. Maybe as a sort of biological control unit or something. And here's why.

KOTM establishes that the Titans have a sort of Alpha-based hierarchy; the most powerful among them is their leader.

But what if humanity found a way to bend that system to our will? What if we had a mechanized Titan of our own, with enough firepower and tech to take them down if necessary, but just organic enough that they'd listen to it...and by extension, us.

@JurassicKaiju14

Yes, that sounds like a very credible theory, and I have heard others a lot like it. That can set up another "don't mess with nature" agenda, which is a recurring theme throughout the Godzilla franchise. I also think that Mechagodzilla will go on some mission to destroy both Godzilla and Kong so that humans can have complete control over the titans like you said, or something along those lines.