Prime VideoThere's a moment in the first episode of Invincible — call it the hinge — where the show reveals what it actually is. For roughly 40 minutes, it’s a cheerful origin story about a teenager named Mark Grayson who finally gets his powers, trains with his superhero father, gets fitted for a costume by a Mark Hamill-voiced tailor, and picks his name. It’s brightly colored, warmly scored, and almost aggressively familiar.And then Omni-Man w…