To get omastar you have to choose the helix fossil when your in mt. moon. then when you get surf from safari zone, go to pallet town and swim all the way down to cinnonbar island and go down to the pokemon lab and go to the 3rd room and give the helix fossil to the professer. after you give him the helix fossil, leave the room and come back and talk to him he will give you omanyte. train omanyte until he is lvl 40 and he will evolve to OMASTAR(omastar is tight)(he is a master and a star)(OMASTAR)