I'm hoping anyone from 1st generation to the 3rd. From Ash, to Gary, to Red our Jesse, James, Meowth from Team Rocket or any other known characters! Cause I'm going to be honest. If they did make an Cameo Appearance, and I suddenly have to battle them, I will literally have a meanie heart attack, and most likely poop myself from my reaction.
Maybe if the new Pokemon is MewThree, Mewtwo may appear, and Ash appears as well stating. "Mewtwo, one of the strongest Pokemon in the World...and I tried to Punch him" Though that was just from the movie, it be funny if that was said in the game XD
OR! maybe a cameo of all the Champions because of an emergency.
Though that's what I wish XD which will never happen :/ sad panda.