Pokémon Platinum Version - Catching Giratina (Altered Form)

If you fail to catch Giratina at the Distortion World, go to the Turnback Cave after you beat the Elite Four. After crossing 3 rooms with pillars, you’ll enter the room where Giratina is. Save your game before you interact with it. Giratina is still on Level 47 and the same new music still plays as you battle Giratina. Make sure you have some Dusk Balls to catch it. After capturing it, you’ll notice that there is a portal that leads to the Distortion World, where you can collect the Griseous Orb. Give the Griseous Orb to Giratina and it will turn into its Origin Form without needing the Distortion World.