Arceus is a white, equine Pokémon with an androgynous appearance. It looks like a qilin or centaur with a gray, vertically-striped underside. This striped pattern repeats on the underside of its mane, tail, and face. Its four pointed feet end in golden hooves. Its long mane extends outward from its head, and its face is gray, featuring green eyes with red pupils and a green circular pattern beneath the eyes. Arceus has a streak of gold coloration on its head and upward-pointing ears. Its neck is relatively long, with two pairs of protrusions on the sides and a flap-like feature on the neck's underside, colored white like much of its body. Attached to its round abdomen is a golden cross-like wheel that changes color along with its eyes and hooves based on its current type, which depends on the Plate or type-specific Z-Crystal it wields. The wheel also has four jewels attached to it. The gray, striated pattern continues past Arceus's waist. Its limbs have gray undersides and extrusions at the tops of the legs. Arceus’s tail resembles its mane in shape and color. Despite its quadrupedal look, Arceus can fly.
According to legend, it shaped the Pokémon universe using its 1,000 arms. Known as "The Original One" in myths and legends, Arceus is considered one of the strongest Pokémon. It is thought to have created Sinnoh and Ransei, and possibly the entire Pokémon universe, along with the lake guardians Uxie, Azelf, and Mesprit, as well as the Mythical Pokémon Dialga, Palkia, and Giratina. Because of this, Arceus is believed to be among the most long-lived Pokémon species. It has the power to recreate the Mythical Pokémon to guard dimensions when a Trainer captures one of them. In the anime, Arceus has been shown to have powers such as restoring what it once destroyed, making things vanish into thin air, halting time, and overturning the laws of nature. The anime also shows Arceus calming Dialga and Palkia and destroying the Red Chain. Arceus can change its type at will by using Plates or Z-Crystals. It can split into two parts, creating a piece of itself outside its home dimension, implying its physical form is only part of its whole being, while its true form remains unknown and incomprehensible.
In ancient times, Arceus cared for and safeguarded the planet, protecting it from cataclysms like meteors. It showed gratitude and compassion to those who treated it kindly. In modern times, Arceus continues to watch over the world, hoping people and Pokémon will work together in adversity. When needed, it provides hints rather than direct intervention. In Pokémon Legends: Arceus, it is explained that Arceus blesses Pokémon to make them more powerful, referred to as noble Pokémon and Ride Pokémon, with power passed down through family lines. The Hisui people worshipped these noble Pokémon. Arceus can also create items for humans, such as the Arc Phone. If betrayed or deceived, Arceus attacks violently and holds grudges. In Arceus and the Jewel of Life (M12), it feeds off the energy of elemental plates. Arceus can appear in dreams and create various Pokémon as challenges, as seen in Eternal Battle Reverie.
In the introduction sequence of Pokémon Legends: Arceus, Arceus took a large, golden, glowing, silhouette-like form while in its homeworld. It was shown capable of human speech and stated that Arceus is simply the name humans call it. The first inhabitants of the Hisui region, the Celestica, worshiped it, calling it "almighty Sinnoh" and "great Sinnoh." Arceus also had the title "might of Sinnoh," with Sinnoh later becoming the region's name. The Diamond Clan and Pearl Clan also worshiped it but mistook Dialga and Palkia for Arceus.
Forms
Arceus has eighteen different forms, one for each type.
(Source: Bulbapedia)
