Ilex Forest (Japanese: ウバメの森Ubame Forest) is a dense forest located in southern Johto, directly west of Azalea Town. The forest's trees are so close together that all light is blocked out, and the forest seems to be in a perpetual night.
There is a shrine for the guardian of the forest, Celebi. In Pokémon Crystal, if Kurt has already examined the GS Ball, placing it in the shrine will cause a level 30 Celebi to face the player. Though the GS Ball was never distributed as an event item outside of Japan, the Virtual Console release of Crystal allows it to be obtained in all regions through normal gameplay. In Pokémon HeartGold and SoulSilver, the Shrine also may initiate a special event in which Celebi will take the player back in time and allow them to battle Giovanni.
Ilex Forest is a winding path through dense trees connecting Azalea Town and Route 34. There are many patches of long grass on the ground where low-leveled Pokémon can be found. Travelers can enter at either end with no trouble at all, but to pass through to the other side they must be able to use the move Cut outside of battle.
When the player enters the forest, the only way to proceed through the next section of the forest is to return a runaway Farfetch'd for the regional cutting master's son, thus receiving HM01 (Cut) as a reward, allowing the player to clear the path from a cuttable tree.
In Generation II, this is done by using the forest's layout to chase it back, using a looped path on the far eastern side, as well as a ledged area. In order to tactically return the runaway Farfetch'd to its owner, the player must corner it and lead it into the direction of the owner.
In Generation IV, there are two Farfetch'd and each needs to be approached while they are facing the other way. The player can do this by walking over sticks and, by doing so, causing them to rustle. This grabs the Farfetch'd's attention and, if no other sticks are rustled, may allow them to be approached from behind. Once the Farfetch'd are returned, the player will receive HM01 (Cut).
In the center of the forest is a man who, in Generation II, will hand out TM02 (Headbutt). Using Headbutt on one of the trees in the forest can sometimes yield a wild Pokémon, which Trainers may wish to capture.
In Generation IV, as Headbutt is no longer a TM, the man is instead a Move Tutor who will teach Headbutt for free an unlimited number of times. Now all trees in all locations can be Headbutted, but not all will yield a Pokémon.
The shrine is a small structure located in the Ilex Forest. It is used in obtaining two event-exclusive Pokémon. It can be found in the deepest part of Ilex Forest, situated right in the center of the forest itself.
Players of Japanese and Virtual Console versions of Pokémon Crystal can place the GS Ball on the shrine, to make a level 30 Celebi appear. The player then has the opportunity to capture the Psychic/Grass Pokémon. In the Virtual Console release, Celebi is guaranteed to have at least 5 perfect IVs.
The forest is much larger in the anime than the games, which is why it was the setting for so many episodes. People are shown to be living in it, and there are small villages scattered throughout, and even a Pokémon Center.
The Ilex Forest first featured in You Ain't Nothin' But A Houndour, where a tree-cutter was doing his shift for the day. When Gold arrived at the forest, he saw the tree-cutter and his Farfetch'd unconscious. A mysterious voice then told Gold to stay away, before revealing itself as the Masked Man. Gold engaged in battle with the Masked Man, and was about to be defeated when the Masked Man saw that the shrine of the forest started to glow. However, the glow then faded due to Gold's intervention, and the Masked Man departed.
The Ilex Forest became the setting of the climax of the Gold, Silver & Crystal chapter, when Lugia and Ho-Oh were passed to Will and Karen, who were told to guard the shrine. Green came to the forest looking for the shrine, and overcame her ornithophobia by sending out the Legendary birds to battle Lugia and Ho-Oh. She was joined by Silver, who had followed her to the forest and was initially held captive by Will, before climbing onto Lugia to battle him. The Masked Man was on his way back to the forest having obtained the GS Ball recipe from Kurt at the Indigo Plateau, but Gold chased him and finally defeated him in battle, forcing him to reveal his identity. Using the timely intervention of Pika, Chuchu, and their egg, Pryce completed the GS Ball and started to travel in time. Gold eventually used the newly-hatched Pichu to enter the time void, while it was still open, to chase after Pryce.
Meanwhile, Red and Blue arrived at the forest from underground and joined the battle on Green's side. They witnessed countless Pokémon, sent from the Pokémon Storage System gathering to connect with Lugia and Ho-Oh, freeing them from the Masked Man's control. Yellow arrived, having been chased all the way to the forest, followed by Crystal who teleported to the forest using the Legendary beasts. Gold (who had been trapped in time), as well as Silver and Crystal, eventually entered the shrine, into the crack in time with the Legendary beasts to follow Pryce. At the end of the battle, Will and Karen accepted an offer to work alongside Koga and Bruno.
The Ilex Forest also played an important role in the plot of the HeartGold & SoulSilver chapter. Celebi helped Pryce out of the crack in time after he foresaw the destruction of the future caused by Arceus's creations. At the same time, Giovanni was at the forest looking for a cure for his illness. He saw Pryce and attacked him for what he did to Silver, but Lance intervened and convinced the two to work alongside him. Before heading to the Sinjoh Ruins, Giovanni stationed the Team Rocket Elite Trio to guard the forest while Celebi gathered the cure.
In the Generation II games, the Pokégear's map made it appear that a route existed between Azalea Town and Ilex Forest, even though this is not the case. This was corrected for the map in Generation IV.
"Ubame" comes from ウバメガシ ubamegashi, Ubame oak (Quercus phillyraeoides), a species of tree used to make binchōtan charcoal.
"Ilex" is the genus of holly. Considering its Japanese name, it may also be derived from Quercus ilex, the holm oak or holly oak, another tree commonly used in charcoal manufacture.