On this obscure Blunderzag thread ,we figure out how this works. This boy literally has a plate over his internal mouth which is itself covered by an external mouth.
How does he do this?

 

Speakers, my dude.

 

He's a ventriloquist.

 

Why do these robots have mouths in the first place? And how do they move like skin despite being metal?

These are questions that break the mind if you ask them.

 

Some sort of solid skin idk

 

What if his mouth plate opened up like Primal's and he fit his jaws into place to work the outer faces mechanisms. It's just like those Halloween masks that open their mouths and stuff.

 

What if he were a robot and had mechanical parts in his overarmor that worked as an extension of his regular body?

 

It’s called soft organic metal

Think colossus from the X-men

 

It doesn't even have to be solid metal, it could be a metal mesh with actuators underneath.

 

The idea that the plate covers a mouth is just canonized fanwank.
In it's origin, the plate is the mouth.

 

It's just a cool poster to symbolize Magnus's heritage.

 

Seriously, speakers.

No need or use for working tongue and vocal cords on beings who do not breathe.

 

...With his mouth?

Also uhhhhh...

I just noticed he's rockin' out with his "Magnus" out.

 

You ask one rhetorical question and everyone seems to crawl out of the woodwork to answer it.

 

I always figured that any sort of combining would shut down unnecessary systems or change their function. As for speaking with a mouth plate, sound is nothing more than vibrations so a machine could resonate metallic plates and since they’re alien, that seemingly metal plate might be a lot more advanced even though the cartoons wouldn’t lead you to believe that. But I’d agree with the idea that maybe there is a techo-organic bot under the transforming bits which are more like armor.

 

They are robots, everything is basically different devices. They connect to it and the supermode head becomes the primary device for speech output.

 

Nano technology. Looks like if the metal is soft.

 

Just like how he speaks in truck mode. In certain modes different things are used instead of others .

 

He can't deal with that now!

 

With his eyes, I think.