Well, it's a verse where there are only 12 universes, so in other mythos' he may just be multiversal.
And yeah, he showed up at the end of episode 40. And the preview shows this dragon:
Originally posted by XSUPREMEXSKILLZ
Are these things I can view with my own two eyes? And omniversal is a pretty ****ing hefty level of power to attain. Like, TOAA might not even be omniversal.
TOAA's the author, so he can write himself as whatever he wants, including "I'm omniversal". Even if he isn't omniversal.