Clearly you haven't studied cryptography, and that's actually good, as a cryptographer can't really think out of the box, but you're not in the box to begin with.
Anything you could 'invent' that involves rotating letters in the alphabet, whether or not depending on the character position, and weather or not linear, is a mono-alphabetic substitution cipher. (my bad for mislabeling it as Caersar cipher earlier.)