Metal sonic is the first rival battle in the game and one of the easiest to bypass. First off never stop running. ever during this fight. quickly tap x to do a quick spin boost to get back up to speed if your hit but dont relay on it.  Also he has 4 stages of attack each are pretty easy to dodge save the second. on the first just keep running and he will fly behind you and attempt to ram you simply jump and hit him as he flys underneath you. on the second attack he throws lightpoles at you simply stop short of where they hit and continue and hit him as he tires. third he will hover to the right side of the screen and produce a large electric shield if your quick you can knock him out of it if you attack as soon as he starts it up. Its one of the simpler fights in the game