Please correct me if any of these statements are wrong.
16 Engineer is the Mustadio that joins the party.
22 Engineer is ONLY USED BY THE GAME during the cut-scene / guest Mustadio, and nowhere else. Editing it's stats does nothing to the rest of the game.
22 Engineer is Guest Mustadio, not just used in Cutscenes, odd that the guest has innate Maintenance, eh?