We have already gone over getting Palkia, Dialga and Giratina and Reshiram, Zekrom, and Kyurem, so now it's time for another set of Legendary Trios, the Forces of Nature – Tornadus, Thundurus, and Landorus.
To catch these three you will need to make use of trading Pokémon and the items/Pokémon you get by going through the Pokémon Omega Ruby and Alpha Sapphire story: the Eon Flute and the free Castform you received from the Weather Institute near Route 119.
If you missed out on grabbing Castform, don't worry, you can head back to the Weather Institute on Route 119 with an empty slot in your party and talk to a scientist there and boom — you've got yourself a castform.
While Castform is in your party, use your Eon Flute to Soar near Fortree City, you should see a huge dark storm cloud in the sky — head over to it and go inside. Once you are inside you will come across either Tornadus or Thundurus. Which Legendary Pokémon you come across depends on which version of the game you bought.
- Omega Ruby: Tornadus
- Alpha Sapphire: Thundurus
Once you have capture one of the two use the trade system to get the one that you are missing (if you captured Tornadus trade another Pokémon for Thundurus).
Put both Tornadus and Thundurus in your party and take to the skies above Fortree City once again. There should be yet another storm cloud in the sky (in the same location as the previous), head over to it and step inside. Once you are inside of the storm cloud you will come across Landorus.
Don't forget to bring HP restoring items and plenty of Poké Balls to your legendary battles.
Here's where you can find more guides for catching legendary Pokémon and finding Mega Stones.
