How to catch Giratina in Pokémon Legends: Arceus?
There are four giant Pokémon in the Sinnoh region: Dialga, Palkia, Giratina, and Arceus. You have to beat the first two to beat Legends: Arceus, but that leaves Giratina and Arceus still waiting for you. These two require a lot of work to unlock and then eventually capture, but it's doable.
How to Unlock Giratina
As with most Pokémon games, some great mythical and legendary Pokémon are still waiting to be captured after you've cleared the main storyline. In Pokémon Legends: Arceus, the last large Pokémon you can catch is Giratina, as long as you do three things:
Beat the main story. Once you see the credits rolling in, you'll know you've done the work.
1. Grab Azelf, Mesprit, Uxie, Heatran, Cresselia and Regigigas and collect all the plate armor.
2. Go back to the Ancient Retreat and talk to Cogita.
3. She will mention that she needs three pieces of wood for some reason. If you don't have three in your bag or storage box, you can find some at:
Obsidian Fieldlands: Head to the north side of the Deer Trail trail to find it.
Crimson Minelands: Look south of Arena Brava.
Cobalt Coastlands: Head to the coast between Windbreak Stand and Castaway Shore and you should see some.
Coronet Highlands: Head to the north side of Paradise Lookout.
Alabaster Icelands: Climb up to the glacier platform and you should see some lying there.
After giving her the wood, she will give you a sprite sheet.
Go to Jubilife Village to buy the best potions and resurrection potions if you haven't already.
Go to Coronet Highlands and head to Celestica Ruins.
It is strongly recommended to save manually at this time!
Now head to the summit of Coronet where you saw Dialga and Palkia before.
surprise! Volo is obsessed with Giratina and Arceus and has a crazy hairstyle to prove it. You will have to fight Volo. This will be a very tough fight. Bring your best Pokémon to the table and use his Pokémon's weaknesses against him.
Spiritomb (Lv 68) Weakness: Fairy
Roserade (Lv 68 ) Weakness: Psychic, Fire, Flying, Ice
Hisuian Arcanine (Lv 68) Weakness: Rock, Fighting
Lucario (Lv 68) Weakness: Fighting, Fire, Ground
Garchomp (Lv 68) Weakness: Fairy, Ice, Dragon
Togekiss (Lv 68) Weakness: Steel, Ice, Poison, Rock, Electric
You'll want to make sure to use Max Revives and Max Potions as often as possible throughout the fight. This is by far the toughest segment in the game. Once you defeat Volo, Giratina will appear and you will have to fight Giratina.
How do trainers go to fight Giratina?
While fighting, the Giratina Altered Forme will reach level 70. You can't catch it here, so just try to beat it. You will be able to grab it later. I highly recommend that your team be level 65 or higher in this battle.
Trainers can take advantage of Giratina's weaknesses to defeat them faster.
Giratina Altered Forme (Lv 70) Weakness: Dark, Fairy, Ghost, Ice, Dragon
Don't get too excited when you get its health down the first time. It is now in its original form and has full health again. Its weaknesses are the same, so keep fighting it as before. You need to make sure to use potions and resurrections to keep your team alive. Once you defeat Giratina's Origin Form, it disappears and your flute turns into an azure flute so you can fight and catch Arceus.
Don't worry, you didn't get scammed by catching Giratina. But you'll need to fight it again to sync it into the Poke Ball. Speak with Professor Lavington near the gate of Jubilife Village. He'll tell you he "saw a huge shadow" which he thinks is Giratina.
Go to the Cobalt Coastlands and go to the Spring Path in the northwest corner of the map. Enter the Turning Cave and you will encounter Giratina.
To be honest, I think it's a bit of a hassle to get Giratina this way. Of course, there will be players who will like this challenge. The easiest and most direct way is to buy Giratina at PKMBuy, there are also many Legendary, Alpha Pokémon you want.