From Bulbapedia, the community-driven Pokémon encyclopedia.
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 games.
CoroCoro's editions containing pre-release information of the games depicted earlier sprites for Silver, Chikorita, Pikachu 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.
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.