Is not a good idea rely in one poke for win pal, metagross is great and is a powerful attacker but (like i prove in our second battle), you can bet him quickly -faster Jynx, Focus Blast = Fainted Metagross...
Try that strategy but instead only rely in Mgross, have a B plan (like your Tyranitar or, if the opponent agree in use, your Lugia)
I'm going to make my metagross even MORE dangerous by having a pokemon with belly drum an baton pass, because baton pass carries all stat-ups, and belly drum MAXIMIZES attack.