They have been called the Creation Trio, the Dragon Trio and the Deity Trio, each control an aspect of the Pokémon universe; Dialga controls time, Palkia controls space, and Giratina controls antimatter. Did you know Pokémon went that deep?
To capture the trio you will need three things: to have captured Uxie, Mesprit and Azelf, the ability to trade Pokémon and Soar.
We have been over how to capture the Legendary Lake Guardians, Uxie, Mesprit and Azelf – but you don't necessarily need to have captured them in Pokémon Omega Ruby or Alpha Sapphire in order to start your journey for Dialga and Palkia, acquiring them through a Pokémon Bank transfer will suffice as well.
Take the three Lake Guardians out Soaring on a trip toward Dewford Town, on your flight you will come across a tear in the sky. The tear is a sort of spacial tear between realities and who you encounter inside depends on what game version you have.
- Pokémon Omega Ruby: Palkia will appear.
- Pokémon Alpha Sapphire: Dialga will appear.
In order for you to get Giratina you need to have both Palkia and Dialga in your party, considering that it is not possible to do in one game – you need to get someone to trade with. Get yourself the Pokémon you require and head back to the skies near Dewford Town with both of the legendaries in your party.
There will be another spatial tear in the sky, go inside and grab yourself a Giratina.
Don't forget Poké Balls and Full Restores.
Here's where you can find more guides for catching legendary Pokémon and finding Mega Stones.