From Bulbapedia, the community-driven Pokémon encyclopedia.
The Ilex Forest shrine is a small structure located in the Ilex Forest, which it is named after, west of Azalea Town in Johto. It can be found in the deepest part of Ilex Forest, situated right in the center of the forest itself. Many people say that the shrine is a symbol of good luck, and wards off evil spirits in the forest. Some others say that the shrine is linked to the legendary Pokémon, Celebi, and that it lives inside the forest shrine, as the forest guardian.
In the games
The shrine is present in Pokémon Gold and Silver, but has no purpose. In Pokémon Crystal however, it is used to obtain the legendary Pokémon, Celebi. When the player puts a GS Ball on the shrine, a level 30 Celebi will appear. The player then has the opportunity to capture the Pokémon. However, due to a forgotten Pokémon event in the English version of the game, it is not possible to obtain and capture Celebi.
In the Japanese version of Pokémon Crystal, the Goldenrod City Pokémon Center is replaced by a larger building called the Pokémon Communication Center which includes the machine to use this feature. Another feature in the Pokémon Communication Center is the Pokémon News Machine, which compiles news from the save files of players across Japan. Reading the news would sent out a player's own save file data, allowing other Trainers to read about the player's adventure. The system had a special mobile event which allowed players to obtain the GS Ball. This item, given by a nurse in the Pokémon Communication Center in Goldenrod City, may be taken to Kurt in Azalea Town to investigate. After a day passes, taking the GS Ball to the Ilex Forest shrine summons a level 30 Celebi to battle. The player then has the opportunity to capture the Psychic/Grass Pokémon.
Due to the lack of the Pokémon Mobile System GB in the English version of the game, there is no way of getting the GS Ball, via this communication. However, it is possible to obtain this event by hacking or glitches within the game. In the Japanese version of Pokémon Crystal, players could use the Pokémon Mobile System GB to obtain a GS Ball as an event item which they could take to Ilex Forest. Using it at the forest's shrine would prompt an encounter where a wild Celebi could be captured. However, no equivalent event was ever offered to players of the English version of the game. Some game-enhancing devices, however, such as the GameShark, can be used to generate the GS Ball right in the player's bag in both languages. It was never implemented outside of Japan, likely due to the fact that cell phones were not as advanced or popular in other regions at the time.
The shrine appears in the remakes of Gold and Silver, in the same location as in Generation II, in the Ilex Forest. Spiky-eared Pichu will appear at the Ilex Forest shrine and will join the player's party if the player approaches it with the Pikachu-colored Pichu. A Pikachu or Raichu evolved from this Pichu will also activate the event.
If the shrine is approached with a promotional event Celebi as the partner Pokémon, Celebi will take the player and their friend back in time - first to see Giovanni leave his son Silver after being defeated in Kanto, and then further ahead in time to battle and defeat Giovanni to prevent him from reuniting with Team Rocket during their takeover of the Goldenrod Radio Tower.
In the anime
In the anime, the shrine has briefly appeared in A Farfetch'd Tale, and another shrine appeared in the fourth movie, Celebi: Voice of the Forest, strikingly similar to the Ilex Forest shrine. In Celebi and Joy, a shrine that resembled the Ilex Forest's shrine resided in Marion Town.
The first appearance was during A Farfetch'd Tale, when Team Rocket gets lost and hungry in the Ilex Forest. Meowth smells food nearby and they find the small Ilex Forest shrine where two dumplings have been left. Jessie snatches one, Meowth the other, leaving James empty-handed. They spot a Farfetch'd—Sylvester's—wandering around, and knowing that it's very rare and valuable, plan to catch it and sell it to the highest bidder. After Team Rocket leaves, Ash and co. come to the shrine, and Sylvester says it's a shrine to the spirit that watches over the forest. In order to find the lost Farfetch'd, they all run in different directions, and agree to meet back at the shrine in an hour.
Another shrine appears in the fourth movie, Celebi: Voice of the Forest. Although it isn't the same Ilex Forest shrine, it does contain the same qualities. It is found in the deepest part of the forest, and many people say that the shrine is linked to the legendary Pokémon, Celebi, who supposedly lives inside the forest shrine, as the forest guardian. The first time the shrine is seen is when Sam runs into it before Celebi transports him into the future. The second time it appears is after he transports to the future.
The third shrine appears in Celebi and Joy, when Ritchie and Sparky save a young girl Joy hanging from a cliff, and manage to save her and pull her back up with some help from her Rapidash. Joy explains that she saw some flowers that she wanted to pick for Celebi when she fell. She explains that legends say that a Celebi lives in this forest, and she thinks it's true. To prove it, she shows them a Celebi Shrine that was put up in the forest a long time ago. Later that night during a thunderstorm, Nick's father is informed that Joy ran into the forest. As Ritchie and Nick head out to look for Joy, they find her unconscious near the shrine. As a fire starts near them, a Celebi appears and protects them.
In the manga
In the Pokémon Adventures manga
In Houndour from the Dark, after being attacked by a wild Farfetch'd, Gold quickly tells his Pokémon to run away from an advancing Wing Attack. They arrive at a small wooden shrine, which happened to be the Ilex Forest shrine, and decide to take shelter behind it. Later, in The Ariados up There, the little wooden shrine Gold hid behind earlier suddenly starts to glow, and Masked Man instantly stops his pursuit of Gold to make his way towards the shrine instead. However it stopped glowing before he gets there, concealing its secrets again.
Later, they returned to the shrine for the final confrontation. Celebi was captured in the GS Ball, and the combatants entered the timestream by passing through the shrine’s doors. After defeating the foe and apparently becoming lost in time, Gold appeared from the Shrine, to everyone’s surprise.