First he will ask you what color rock green blue or red ether one gives you a Pokemon blue mudkip, green treeko, and red torchic.after you get it you probably won't see him again :)
He goes to the museum which is in pewter city.
Stephen Sorrentino goes by Even Stephen.
in the cave above Deford city
That 'invisible thing' is a Kecleon. You need to obtain a Devon (Hoenn equivalent of Silph) Scope, from Stephen. Go out past Fortree City and go to the bridge. I'm fairly sure you will find Stephen there.
Stephen Shields goes by Steve.
He goes to the museum which is in pewter city.
at meteor falls
it is a cave
Stephen Sorrentino goes by Even Stephen.
in the cave above Deford city
That 'invisible thing' is a Kecleon. You need to obtain a Devon (Hoenn equivalent of Silph) Scope, from Stephen. Go out past Fortree City and go to the bridge. I'm fairly sure you will find Stephen there.
Stephen Schwarz goes by Steve.
Stephen Bettles goes by Stevie.
Stephen Roloc goes by MacGyver.
Stephen Pitkin goes by Doots.
Stephen Polk goes by Steve.
Stephen Niver goes by Niver.