Catch Giratina

Along with Dialga and Palkia, Giratina is a member of the creation trio. You can find this Legendary Pokemon by heading to Route 214 (south of Veilstone City) and going east towards the Spring Path—you’ll reach a hidden area called Sendoff Spring with an entrance to a cave. Explore Turnback Cave until you find Giratina - it’s basically a randomly generated cave. Specifically, you need to find the third pillar before entering 30 rooms, then Giratina in its Altered Form will spawn in the next room you enter. Giratina will be Lv. 70 and can heal with Pain Split, so be prepared.

Once you’ve caught Giratina and unlocked Rayquaza inside Ramanas Park, you can battle Origin Forme Giratina inside the Distortion Room to acquire the Griseous Orb—It boosts the power of Dragon and Ghost-type moves when held by Giratina, and changes Giratina into its Origin Forme.