Ok I have beat the elite four and I'm at the place called sendoff spring.someone..

Go into sendoff spring you will find a big lake go behind it use rockclimb go inside the cave it is a maze cave you will need rocksmash the cave is turnback cave you will find giratina there it is genderless type ghost/dragon and level 70 attacks shadow force, slash, earth power, and heal block enjoy don't forget to use duskballs

If you go into the Turnback Cave at the spring's basin, you can catch Giratina

Giratina is a Lv.70 Ghost/Dragon that knows: Shadow Force, Heal Block, Earth Power, and Slash so go inside prepared.

Go catch the legendary at the 30th floor.

Use rock climb up the side and then go to the back and rock climb down. It's a complicated place and you need rock smash. When you find the first pillar, just go to the door behind it and keep on passing each pillar. Eventually you should find giratina. Be prepared.

Giratina Lv. 70
Shadow Force Heal block
Earth power Slash

Sendoff Spring?

I know Spring Path? In there, there's a cave, right? It's Turnback Cave. After maneuvering through random doors, since the place itself is random, and after you pass 3 pillars, the next room will be where the level 70 Giratina resides.