Moltar says he's never introduced at the beginning of the show, but he's been introduced at least once before.
Space Ghost: So anyway, Moltar, I'm always open to ideas which might make the show better.
Moltar: How about I come out at the beginning of every show and hit you upside the head with a hammer?
Zorak: I'd watch that show.
Space Ghost: Alright, it's settled. Zorak is the hammer, Moltar, you suck.
Crow: CAW! CAW!
Space Ghost: Ah, yes.
Zorak: Knock Knock.
Space Ghost: Who's there?
Zorak: **** You.
Space Ghost: ...(laughs) Well done, Zorak!