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Pokémon HeartGold and SoulSilver
, as remakes of Pokémon Gold and Silver
, implemented redone elements of the original games. Nonetheless, as individual games, they have gone through similar stages of development as all the other core series
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Reason: What is Cyndaquil's beta front sprite while the opening of the games.
's editions containing pre-release information of the games depicted earlier sprites for Silver
and Pikachu-colored Pichu
. Chikorita's leaf was darker.
An earlier back sprite for Ethan was also shown. His hair was slightly different and there was a symbol on his hat. There is also a prototype sprite for Lugia.
In addition, there is a Shiny sprite for the Spiky-eared Pichu within the coding of the games. However, it's impossible to legitimately obtain such form, due to the fact that this Pokémon is assigned a fixed personality value.
Earlier screenshots also depict the Slowpoke Well with a Team Rocket Grunt standing where Proton is in the final release, as was the case with the original Pokémon Gold and Silver. Another screenshot depicts the Mystri Stage in the Sinjoh Ruins with the three circles being identically colored. In the final release, they have three different colors specific to each circle.
Cyndaquil's front sprite in the opening of the games is different from its front sprite used during regular gameplay.
All items present in the internal data of Pokémon Diamond and Pearl and Pokémon Platinum are found in Pokémon HeartGold and SoulSilver, in addition to the latter's exclusive items.
- Photo Album, a Key Item for storing photos. It was replaced with photo storage integration in the PC;
- SlowpokeTail, an expensive but useless item. It makes a comeback from the original games and can be obtained through modification of the saved game but it has no function. Interestingly, it was made a Key Item (it was a regular item in the Generation II games).
The same debugging tools found in the internal data of Pokémon Platinum are also present in Pokémon HeartGold and SoulSilver.
A PokéGear icon that resembles Kris was discovered in leftover data.
Unused map description data in the Pokégear exists for several locations.
- Lavender Radio Tower: "An old building that has been reused as a radio broadcasting tower."
- Battle Frontier: "A Battle Stadium with five different sets of rules to enjoy."
- Mt. Silver: "A mountain where something mysterious awaits you underfoot."
- Pokéathlon Dome: "A place where Pokémon can compete against each other's strengths."
- Bellchime Trail: "A path said to always be bathed in sunset, no matter what the season."
In the Japanese versions, the descriptions for Rocket Hideout, Goldenrod Tunnel, Dragon's Den, Cliff Cave, KGR Map, and Route 23 have the generic development text "Dummy Guide Message" (Japanese: ダミーのガイドメッセージ) followed by the location's name.
Head Smash Nosepass
Nosepass has Head Smash listed as an Egg move but is not able to breed with any Pokémon that knows this move making this egg move impossible to breed onto a Nosepass.
If the game detects it is being played via a flash card or emulator, it will freeze during one of the first Trainer battles with the Poké Balls spinning indefinitely.
References to Pokémon Gold/Silver
There are two references leftover in game referring to the original Generation II games. However, the wording or reference has been altered in such a way that is no longer relevant.
Kurt used to only be able to produce one Poké Ball at a time in Gold and Silver but in Crystal and HeartGold/SoulSilver he is able to make multiple Poké Balls at one time. However, he still refers to the multiple Poké Balls being made as a singular Poké Ball being made regardless.
Lucky Channel advertisement
In the Goldenrod Radio Tower, on the first floor; there is still an advertisement on the wall for Lucky Channel which was a radio channel in the Generation II games the player character could tune in to. The channel was replaced with Felicity who gives the player prizes if their Trainer ID matches with that of the Pokémon. However, in the original Japanese releases, the wording for the Lucky Channel advertisement is altered to make it seem like it may have either been an upcoming or scrapped radio show. 
Due to legal issues related with gambling, the interior design of both Goldenrod and Celadon Game Corners was completely overhauled in all non-Japanese releases of Pokémon HeartGold and SoulSilver. However, the original design is still present within the internal data of the localized releases, despite being severely limited, since most dialogue scripts were removed (with the exception of the Coin purchase interface, which is still completely functional and translated) and the slot machine interface pointers are redirected to the Voltorb Flip interface instead.