The final Boss has six Pokemon to be snagged: Rhydon (level 46), Zapdos (level 50), Tauros (level 46), Exeggutor (level 46), Articuno (level 50), and Moltres (level 50). Go to the Outskirts and buy twenty of every kind of Pokeball. You should also use your Shadow Pokemon against his and they will not do very much to each other. Additionally, in the final battle with Greevil, if one or more of the Shadow Pokemon faint, do not reset. Just win and fight him again. He will have the one(s) that you missed, and the rest will be normal. Also, if you already have Shadow Lugia, you will only battle Greevil.