Within the games' data is a scrapped map for a dense, maze-like forest leading up to Mt. Silver. Since the mountain is inspired by Mt. Fuji, the maze is likely derived from Aokigahara, a forest at the base of Mt. Fuji that is famous for its density and natural soundproofing. Because Aokigahara is also notorious for its popularity as a suicide site, it's likely that the maze was removed in favor of a shorter, more conventional route to avoid stoking controversy from Japanese audiences.

Because of an oversight, the Fast Ball, which is supposed to work better on Pokémon that have a proclivity to flee, only works as it should on Magnemite, Grimer, and Tangela. This is because the Ball is supposed to look for three categories of Pokémon: ones with a 10% flee rate, ones with a 50% flee rate, and ones with 100% flee rate. However, for some reason the ball only chooses the first three Pokémon in the first category (10% flee rate) when it applies its catch-rate modifier.

If you get the Dragon Fang through trading or by hacking it into the game rather than getting it from the shrine within Dragon's Den, Clair will call you out for cheating and will not give you the Rising Badge until you get the Dragon Fang yourself:

According to Ken Sugimori, the Pokémon that appeared in the front page of the 1997 edition of MicroGroup Game Review showcasing Pokect Monsters 2 were not supposed to appear in the game at all. While some were never to be seen, Tyranitar ended up being used. This explains why Tyranitar wasn't in the leaked 1997 prototype ROM.

Originally, the region of Johto was based on the entirety of Japan, rather than just the Kansai region, with towns and dungeons based on areas within the country, such as Hokkaido (called North in the Spaceworld 97 demo), Osaka (which was called West and likely became Goldenrod City) and Mt. Fuji (which likely became Mt. Silver). Due to this, Kanto, which was based on the region in Japan of the same name, was compressed into a single map, with Blue as the Gym Leader.

Evolved and pre-evolved forms for Tangela, Qwilfish, Goldeen, Vulpix, Paras, Ditto, Doduo, Meowth, Mr. Mime, Growlithe, Lickitung, an alternate evolution for Weepinbell, Farfetch'd, Pinsir and a Grass type evolution for Eevee, were implemented in the demo featured at Nintendo's Spaceworld 97 show. All of these evolutions were cut from the final product.

Gold and Silver originally had a completely different looking starter trio. They were Happa (grass), Kurusu (water) and Honōguma (fire). The grass starter's design remained somewhat similar in the final release, becoming Chikorita.

The song for the Bicycle theme is actually a sped up version of the Goldenrod City theme with different instruments.

In this generation, Smeargle's normal and shiny colors are reversed - its shiny being green instead of red. Pokemon Stadium 2, Pokemon Colosseum, and Pokemon XD: Gale of Darkness also have this issue. Pokemon Colosseum and Pokemon XD: Gale of Darkness have this issue because they reuse models from Pokemon Stadium 2.

Due to a glitch in the game's code, burn, paralysis and poison statuses don't affect the catch rate of a Pokemon.

Because of a glitch in the game, Moon Balls don't work as they were planned to. Moon Balls were supposed to increase the catch rate (x4) when trying to catch a Pokémon that evolves using a Moon Stone. Instead, they were programmed to increase the catch rate when you try to catch a Pokémon that uses a Burn Heal (an item not related to evolution at all) to evolve.

There's an unused script that triggers a battle with a level 40 Entei upon contact. It might be that early in development, the Legendary dogs would have been battled normally like the legendary birds in Gen 1 instead of searching for them in the grass.

At one stage in development, it was possible to name the player's mother.

When the NPC Trainer Firebreather Dick at the Burned Tower is defeated, his overworld sprite pallete changes to black and white until the player exits and reenters the area.

The clouds on Gold's title screen and the sea floor on Silver's title screen are just recolors of the same image.

Lance's Aerodactyl knows Rock Slide. This is odd as Aerodactyl could not learn Rock Slide until Ruby and Sapphire.

The map of the Pokémon Laboratory on Cinnabar Island can be found complete in the data for Gold and Silver. This could suggest that there were once plans to include the laboratory in the game.

Most of Pokemon Gold and Silver's music was created on an Amiga computer, converted to MIDI, and then reconverted to the game's music format. Some songs, though, like the Unown radio music, were created by hand directly in the GSC music format.

The Love Ball, a special kind of Pokéball, has a description of "For catching the opposite gender." Due to a glitch in the game's code, the effects are 8x as effective if used on a Pokémon of the same species and gender as the player's Pokémon.

Red's party in the Generation II games is based heavily on in-game events from the Generation I. Charizard, Venusaur, Blastoise, and Pikachu are available in all iterations of the original Kanto plot. Espeon could have been obtained as an Eevee in Celadon City, and Eevee notably serves as Blue's starter in Pokemon Yellow. Lapras is given away by a Silph Co. employee, and two Snorlax are required to be caught or defeated in order to travel to Fuchsia City. Furthermore, in the Generation II games, only the Snorlax that was previously blocking Route 12 (now blocking the entrance to Diglett's Cave) is available to the player, suggesting that Red defeated it and caught the one blocking Route 16. His party in the Generation II games also matches that of Red in the Pokemon Adventures manga during his venture to Mt. Silver, although Pokemon Adventures' Red borrowed Charizard and Blastoise temporarily from the characters Blue and Green, as he didn't own those Pokemon.

Only the Black Belt and Magnet's descriptions say, "Boosts Fighting-type moves. (HOLD)" and, "Boosts Electric-type moves. (HOLD)" instead of, "Powers up Fighting-type moves. (HOLD)" and, "Powers up Electric-type moves. (HOLD)" like every other type-enhancing item.

In the fight against Lance, he has 3 Dragonites, two of them are LVL.47 and one at LVL.50, which is not possible as Dragonair doesn't evolve until LVL.55.

Both early artwork of Bellossom and its Gold and Silver artwork show that it was originally a similar color to its other evolutionary relatives. A possible explanation for the change to its current color scheme would be the intention to avoid another racial controversy, as the original Bellossom design appears similar to traditional polynesian dress. However, this is unlikely to be the case.

The unused Bird type from the Generation I games remains in the Gold & Silver's code. This is presumed to be a carryover from the Generation I games' engine, as Pokémon Gold & Silver were developed on an upgraded version of it.

In a MicroGroup Game Review it shows unknown female and male trainers who never appeared in the final game. It also shows 2 unnamed Pokemon and an early version of Tyrannitar.

In Gold, Silver, & Crystal, the shiny Charizard sprite was a light shade of purple with green-blue wings. Starting with generation 3 though, it was changed to black with red wings for unknown reasons.

Pokemon Gold & Silver started out as Pocket Monsters 2. It was planned to come out in 1997, but due to delays and other issues the name was dropped. One year later the game was re-announced as Pocket Monsters: Gold & Silver.

When Red is encountered at the summit of Mt. Silver, he has no dialogue, merely repeating sets of ellipses before beginning the battle. This is a reference to his silent role in Generation I, as he only answered yes or no questions. This trait carried forward to future generations, including the HeartGold and SoulSilver remakes.

In the Ruins of Alph, the PokéGear will lose signal. Accessing the Radio function in this area will, instead of giving you the normal radio songs, give you a haunting sound, which is generally accepted to be the cries of the Unown.

In the code for Gold & Silver, there are various pieces of unused dialogue that refer to an item called "Sweet Honey." This implies that the honey mechanic was planned for Generation II but scrapped to return later in Generation IV.

There were plans to have a skateboard as a type of transportation similar to the bicycle, but it was later cut for an unknown reason.

Olivine City has a hidden map/house that is only accessible by using cheat codes.
The map is of a small house containing two NPCs. The first is a Rhydon, whose glitched sprite changes into a Clefairy during walking animations. When A is pressed in front of it, it simply says, "Gugooh!" The next is a woman, when A is pressed in front of the woman in the house, she says: "When my Pokémon got sick, the Pharmacist in Ecruteak made some medicine for me." It is worth noting that she says that the pharmacy is located in Ecruteak City, when in the final version of the game it was located in Cianwood City.

Also, presuming that the player is in the Olivine House; if the radio is playing "The Pokédex Show" instead of the "Pokédex Talk Show" the game will not display any Pokédex entries and freeze (this will occur between 4am and 10am).

Pokemon Gold and Silver were planned to be the last Pokemon games.

The original starting town in Gold and Silver was called "Silent Hills". It's not known why the location changed, but it could have been to avoid comparisons to the horror game Silent Hill, which was released during Gold and Silver's development.

The gym in Goldenrod City is laid out in the shape of a Clefairy.

A Safari Zone was originally planned to be in the game, but removed at some point in development. As such, if accessed via a glitch or cheating device, there are no Pokemon to be found in the grass, but some can be found via fishing.