Have you been unable too see season 4? because he shows up in a few episodes there. Also if you want too no more about him check out his page.

Thanks I will. Uh what's that in his mouth?

Uh what do you mean what's in his mouth? For now I can assume you are referring to what is inside his armor. Is Armaggon himself. He is literally an alien shark wearing a shark armor.

That's his armor? It looks like his mouth is completely open.

It does look like it, but is the mouth of his armor. His armor is able to transform into a shark, which is sort of his battle mode. Also the mouth does close when he is in his shark mode. When is not, it sort of looks like a hood.

So wait a minute he's a shark?

Yes he is an alien shark and he is a wearing an armor that looks like a shark.

his world must be filled with water

His homeworld is believed to be the Cosmic Ocean?