Arceus

Arceus is the final Pokémon to get in the game and is part of the final mission. After defeating Volo at the Temple of Sinnoh, your Celestica Flute turns into the Azure Flute and you can play it to summon Arceus. However, unless you have caught every other Pokémon in the region, you cannot continue on.

Return with your Pokédex complete (except for Phinoe, Manaphy, Darkrai, Shaymin and Arceus), and you will be able to challenge Arceus. You will get taken up to the Hall of Origin for one final frenzied battle.

You will get given Mysterious Balm, converted from your Arc Phone, and you will need to throw it at Arceus to get to the battle. There are several phases of attack. First is sending a batch of homing minor energy bolts at you which need rapid dodging. Another is a blue shockwave followed by a meteor strike. Finally there's big waves of energy that envelop most of the arena. You can also throw a ball to battle Arceus to have an opening for the balm. After you have defeated it, you will be given a piece of Arceus and its Legend Plate.

Arceus
Level 75
OT:Yours
ID:Yours
??? Nature.
Date of Receiving
Snowpoint Temple. Level Met: 70
Calm Mind
Extrasensory
Judgment
Hyper Beam
Arceus - Pokémon Legends: Arceus

Arceus

While all other plates, and the new Blank Plate, will change Arceus' type to a specific type, which also controls the move Judgment, the new Legend Plate changes things considerably. Instead, when you use this, Arceus will be its Normal-type. However, when in battle, the move Judgment automatically changes type and when used, will automatically change Arceus' type in battle. This type will be a type that will do the most damage on Arceus while also taking the least damage from the opponent's native type.

Legend Plate Arceus - Pokémon Legends: Arceus

Rematch - Dialga & Palkia

After you have defeated Arceus, you will also be able to have a rematch with both Dialga and Palkia, regardless of which one you picked. These will be increased in strength. Defeat them and you will get 5 EXP Candy M for success and 3 Grit Pebbles if you do it without receiving damage

Dialga
Level 85
Earth Power
Iron Tail
Flash Cannon
Roar of Time
Palkia
Level 85
Earth Power
Aqua Tail
Hydro Pump
Spacial Rend
Arceus Battle - Pokémon Legends: Arceus

Rematch - Arceus

Much like the Noble Pokémon, you have the ability to rematch Arceus by returning to the area. This time, while the battle in the field is the same, the Arceus is at a much high level, Level 100 and will change form as if it has the Legend Plate. Defeat it and you'll get 1 EXP Candy XL for succeeding and 1 Grit Rock if you manage to do it without receiving damage

Arceus
Level 100
Calm Mind
Extrasensory
Judgment
Hyper Beam
Arceus Battle - Pokémon Legends: Arceus