After completing the main scenario or rather the first part of the story on Pokémon Legends Arceus, you will have to look for the missing plates help Volo. In the end, you will find yourself going to the Temple of Sinnoh and fight Volo there as he's the one with the last plate. Volo will have six Pokémon.
Fight against Volo
This fight will not necessarily be easy and you should prepare a minimum in order not to lose against his team. Here are the weaknesses of each Pokémon to help you build your own team:
Weaknesses: Ice, Fairy, Dragon
Weaknesses: Flight, Fire, Ice, Psychic
Weaknesses: Poison, Electric, Ice, Rock, Steel
Weaknesses: Fire, Combat, Ground
Weaknesses: Water, Rock, Ground, Combat
With its Flying/Fairy double type, Togekiss is a good counter to Garchomp, Roserade or even Spiritomb. In addition, the latter has access to Calmness if you need to boost yourself or Flamethrower to cover Fire-type weaknesses. It will still be necessary to pay attention to Poison, Rock or Steel attacks.
With his dual Ground/Ice type, he will have a definite advantage over almost the entire team. It will still be necessary to pay attention to Lucario and Roserade which can cause you problems with Plant and Combat attacks.
Second fight: Giratina and Volo
This fight directly follows the first fight and it is not possible to heal between the two or to change Pokémon. This time, it's Giratina that you will face and it will be at level 70.
This fight takes place in two phases . The first where you will face the alternate form and the second where Giratina will be in its original form. There is no possible change between the two phases, when you defeat the first, it automatically changes form during the fight, thus regaining its life.
To beat it easily, you will have to help yourself with Pokémon of the Fairy , Ice , Dragon , Specter or Dark type in order to inflict super effective damage on it. In addition, the Fairy type is immune to the Dragon type. The Normal type can also serve you if you want to avoid the Revenant attack. Togekiss and Mamoswine are also recommended Pokemon against this Legendary. So you should be able to get away with them, but of course you can win with other creatures.
Pokémon Legends Arceus is full of creatures to catch. Whether it's simple Keunotor or legendaries like Dialga or Palkia, Hisui will give you the opportunity to capture Giratina as well.