Just to clarify, this is just poking fun at the fans who think King mouth being shown, especially in newer episodes, is a new thing never done before.

That still leaves the enigma as to why he talks with his mouth closed, though.

Maybe a form of telepathy?

Titan powers

To hard to animate Kings mouth movement

Ventriloquism

First time we were given a good look was in covention, s1e5

Correction, episode 2 when he's eating the scones.

I always forget about the first half of that episode, but yeah, his mouth isn't something new

It’s still kind of weird to see but yeah, we’ve known he has a mouth since the second episode

WEH

Fun fact: his tongue is purple. This detail has been consistent.

You can see his mouth in s1e2, when he eats the scones