How Do I Get Giratina in Diamond?

Begin your journey as a Pokemon trainer, traveling through the land of Shinnoh and collecting the eight gym trainer badges. As you win more battles, your party will grow stronger.

Travel to the newly accessible Victory Road and battle the Elite Four and Grand Champion. You will have to take on each trainer one by one, and each Elite Four member will have progressively stronger Pokemon (level 40 to 60).

Encounter 150 different Pokemon in the Shinnoh Pokedex (Manaphy excluded). This feat will turn your basic Pokedex into the National Pokedex, a list of every Pokemon that has existed in the series.

Travel to Route 214 and head down the new path that has opened up, the Spring Path, branching off from northeast Route 214.

Walk down the Spring Path to Sendoff Spring, then climb the rock wall and enter Turnback Cave. This place is home to many advanced Pokemon. Because Turnback Cave is under the control of Giratina, its paths change each time you enter it.

Make your way through Turnback Cave, looking for three rooms that have stone pillars in them. Every room you enter will have a choice of four doors: the one you just walked through, and three others. If you reenter a door you have just come through, you will be returned to the beginning. Instead, choose a new room to enter; it will either have a stone pillar in the center or be another empty room --- the path is random. Approach each pillar when you find it, and press "A." You only have 30 chances to find all three pillars.

Save your game after pressing "A" next to the third pillar, so that if you lose to Giratina or cause it to faint, you can turn the game off and then back on to try again.

Proceed through any of the three doors you have not walked through in this room to be taken to the chamber where Giratina awaits. Challenge Giratina to a battle by approaching it. Giratina is a Ghost-/Dragon-type Pokemon, so Normal-type Pokemon will be immune to most of its moves.

Attack Giratina with Ice-, Rock-, Ghost- and Dragon-type moves to lower its hitpoints. Avoid causing Giratina to faint by using overly strong attacks or moves that cause a one-hit knockout.

Make Giratina more vulnerable to being caught --- for example, put Giratina to sleep or paralyze it. Additionally, lower its speed so that it is unable to be as evasive as otherwise.

Throw Ultra Balls or Dusk Balls until you catch Giratina. Because it is a legendary Pokemon, you may need several attempts before you finally catch it.