Due to the Azure Flute not being officially distributed, it is impossible to legitimately access the Hall of Origin. The only way it can be accessed is through cheating. It is currently unknown if it is possible to walk to the area through tweaking.
When the player returns to the Spear Pillar with the Azure Flute, he or she will be asked to blow into it every time they step one tile north from the entrance until they catch Arceus. Upon doing so, a glowing staircase will appear, leading to an elevated glass platform high above the Spear Pillar, where Arceus awaits the player's challenge. While the player ascends the staircase, the camera will broadly tilt upward and zoom out, giving the player a unique view of the area below. Stepping onto the edge of the glass platform will automatically initiate the encounter sequence and battle. Should Arceus be defeated rather than caught, it will "disappear from sight" but the Azure Flute can be reused to summon it again.
In terms of game mechanics, when the player accesses the Hall of Origin by blowing the Azure Flute, they are actually no longer on the Spear Pillar but rather in a completely separate location, as evidenced by the screen fade-out transition and the change in location header. That is, the game does not place stair tiles onto the Spear Pillar map, but rather warps the player to a new map containing the stairs where the surrounding area looks identical to the Spear Pillar, exactly down to the cave opening that still leads into the mountain interior. This dispels a rumor that cheating to reach the Hall of Origin would trap the player on the elevated glass platform without the stairs to lead back down.
Like the Spear Pillar, the Hall of Origin is an internal area separate from Mt. Coronet, so the Escape Rope as well as Fly cannot be used to leave the location. However, like the Spear Pillar, it is within the range of Mt. Coronet's strong magnetic field and so Magneton and Nosepass will both evolve here if leveled up.
A colored background means that the Pokémon can be found in this location in the specified game. A white background with a colored letter means that the Pokémon cannot be found here.
Although not by name, the Hall of Origin was mentioned by Archer in With a Little Help From Hitmonchan. When Arceus appeared in front of the four Executives and Crys, Archer explained that the Alpha Pokémon was first found "in a far-off land at the end of a long road, which seemed to continue on and on up into the heavens," obviously describing the Hall of Origin. He also said that it couldn't be understood even if he told where this place was located and what it is called, but the important thing was that since all the Plates had now been gathered in one place, Arceus had come back down to this world.
Trivia
If the Sinjoh Ruins event has already been activated with an eventArceus, another Arceus caught in the Hall of Origin may be used to go back to the Sinjoh Ruins and choose one of the two Pokémon that were not chosen previously. The reverse order is also possible. There is no way to choose the third Pokémon.
Two versions of the Hall of Origin map exist in Pokémon Diamond, Pearl, and Platinum: one is the real location while the other is a "fake" copy. The "fake" Hall of Origin uses Spear Pillar as its theme and can be accessed through the void glitch using "Stickyman's Spear Pillar Hall of Origin" method[1], named after its discoverer. The "fake" Hall of Origin contains no warps or events and no Arceus. (YouTube video)
Regardless, it is impossible to battle Arceus even in the real Hall of Origin except through playing the Azure Flute in Spear Pillar. The usual scripts in the area will not trigger unless the Azure Flute script has been triggered, so arriving at the Hall of Origin through other means will not cause the camera to tilt or zoom while the player ascends the stairs, and Arceus will not challenge the player when they step onto the glass platform. The Arceus sprite still appears, but just as in the actual event, it cannot be directly interacted with. This makes Arceus inaccessible through the glitches that enable access to Darkrai and Shaymin, such as the Surf glitch and the aforementioned void glitch. Additionally in Pokémon Platinum, as with Darkrai and Shaymin, the Arceus sprite will not appear in the area at all unless the player has the Azure Flute in the Bag.
