User blog comment:Violetofen4/Pokemonz! A New Clan, too!/@comment-2182302-20110308080839/@comment-5044191-20110309213409

Oh, Team Galactic? Look for a cave in Mt. Coronet. You'll find either Diagla or Palkia depending on your version of the game, and bring high-level Pokemon and a Master Ball. If you get past Cyrus and his cronies, you'll fight the big legendary. Use the Master Ball at the beginning of the battle.

It'll be hard finding the cave, but catching the big legendary is going to serve you big time against the final gym and the Elite Four.