Arceus

Arceus, the Alpha Pokémon and the Creator God of the Pokémon World, served as an antagonist in twelfth Pokémon film Arceus and the Jewel of Life. In the Pokémon games, Arceus has the highest stats of any Pokémon, and can learn nearly every TM and HM move.

Arceus created the Creation trio (Dialga, Palkia, and Giratina) and the Lake guardians (Uxie, Mesprit, and Azelf).

In the film
In the movie, Arceus exhausted most of his powers to stop a meteor that would have destroyed the world, but a man named Damos helped him to recover. In gratitude, Arceus created the Jewel of Life, which would turn the barren region of Michina into a fertile and prosperous land, but was to be returned some years later. He was then "betrayed" by Damos, who refused to give back the Jewel of Life and attempted to kill him. (It was later revealed that Damos had been brainwashed by Marcus, the movie's real villain.)

A millenia later, Arceus awakens to have his vengeance by destroying Michina, and got locked in a fight against the Creation Trio who tried to protect the city and sent Ash Ketchum and his friends in the past to investigate. After Ash and company save Arceus in the past and bring him the Jewel of Life, the Alpha Pokemon ceases his attack as his altered timeline catches up to him and he recalls Damos kindness and Ash's intervention. He then thanks them for saving him and stopping him before it was too late, and he proceeds to undo the damage he had done. He then bids farewell to Ash and his friends goes back into his dimension.

HeartGold & SoulSilver chapter
The chapter opens up with Gold facing the Pokémon Arceus with his entire team. Despite his best efforts, none of his attacks seem to affect the Alpha Pokémon, which responds by attacking his Pokémon with a powerful roar. He tells his Pokémon to hold on and wait for Silver to arrive and help.

A few weeks earlier, Gold is at Ecruteak City where he attempts to catch up with Silver, only for Arceus to appear and blow away the Ecruteak Gym with its powers. Silver and Morty are knocked unconscious, leaving Gold the only one awake to combat Arceus. Gold attempts to face Arceus, but none of his team's attack are able to damage it. Arceus quickly leaves, angering Gold into following it while taking an unconscious Bugsy along for the ride. They follow Arceus to the Ruins of Alph, where they find an injured Lance.

Lance reveals that he was ambushed by someone, which is why he didn't appear at the Pokéathlon. Lance praises Gold's skill at beating the Pokéathlon, but believes that he will be unable to calm Arceus down due to Gold not connecting with Togebo enough. Angered by Lance's words, Gold goes back to face Arceus when it finally lands. Gold faces Arceus in battle again, only to have the same result as earlier. Arceus uses its powers to create a powerful barrier around them, locking Gold and his Pokémon inside. Arceus continues attacking, forcing Gold to dodge all of its attacks.

Gold reveals that he doesn't intend to give up and wishes to learn more about Arceus. Outside the barrier, Silver and Crystal arrive to help. Reacting to the Plates in Silver's pockets, Arceus opens the barrier to let them in, along with Archer, Ariana, Petrel, and Proton, who sneak inside. Arceus uses its powers to transport all seven of them to a snow-filled area. Upon entering the ruins, they find Arceus being dragged onto a stage by the Four Generals. There, Archer reveals that they landed at the Sinjoh Ruins, a mysterious area where the cultures of Johto and Sinnoh meet.

Petrel forces Silver to hand over the Plates to Archer, who proceeds to force Arceus to use its powers. Gold, Silver, and Crystal attempt to stop him, but are blocked by Ariana, Petrel, and Proton. Archer uses the Plates to force Arceus to activate its Ability, Multitype, so that it can use its various types to attack Gold, Silver, and Crystal. Archer praises the trio for helping them use Arceus for their goals when they were just trying to help Arceus.

Archer has Arceus use its power to create the three legendary Pokémon Dialga, Palkia, and Giratina. Silver attempts to distract the Four Generals by feigning suicide, allowing Gold and Crystal to attack while their guard is down. With the assistance of Silver's Feraligatr, Gold and Crystal destroy the legendary Pokémon before they fully form with the Ultimate Attacks. With the three Pokémon destroyed, Arceus retaliates against the Four Generals by blowing them away and absorbs the Plates into its body.

Although they believed themselves to have won the battle, the Pokémon Arceus created quickly reform themselves. Archer reveals that once the creation process begins, it cannot be stopped, and was only halted temporarily so that Arceus could complete itself. Although the situation seemed hopeless, Lance arrives with two allies, the former enemy Pryce, along with the leader of Team Rocket, Giovanni. The three Trainers begin combating the Pokémon, and manage to hold them off for a little while. When Gold questions how Pryce returned, the man reveals that the one who saved him from the crack in time was Celebi, who could see the destruction that Arceus would bring with the legendary Pokémon it created.

After everyone else leaves to take their battle outside, Gold remains in the Sinjoh Ruins to calm Arceus down. Gold sends out his entire team to try and face Arceus, but they are quickly swatted away and defeated again. The only one left standing is Togebo, who Gold refuses to let fight as he does not fully trust in his power. Despite this, Togebo refuses to listen to Gold's commands and continues to hopelessly attack Arceus.

Seeing how determined Togebo is causes Gold to remember how they are both treated as last resorts, which puts them in similar situations. Gold decides to trust in Togebo, and sends him to attack Arceus. Togebo evolves twice into Togetic and Togekiss, respectively, and delivers a Double-Edge attack, which doesn't hurt Arceus, but calms it down enough to end its rage. With the battle over, Arceus flies to parts unknown, but Gold decides to follow it to give Arceus a proper send off.

Trivia

 * Many fans compare Arceus to God, as both are creator gods & supreme beings worshipped by many. Like the Maltheistic portrayal of God, Arceus in some versions have been shown as a tyrannical deity who wants to destroy humanity.
 * Arceus' appearance is loosely based on Kalki, the final Avatar of the Hindu god Vishnu.