Heart Gold and Soul Silver

1. These games will mark the tenth anniversary since the release of the original Gold and Silver Versions for Game Boy Color.
2. As remakes, these games have been speculated since the release of Pokémon FireRed and LeafGreen.
3. The games' engine seems to be based on that of Pokémon Platinum. The reverse happened in Generation III, where Pokémon Emerald was based on FireRed and LeafGreen's engine.
4. As Gold and Silver were considered sequels to Red and Green, HeartGold and SoulSilver are thus sequels to FireRed and LeafGreen.
5. Like FireRed and LeafGreen, as well, HeartGold and SoulSilver implement features introduced in their namesakes' third version (though the only major change from Red and Green to Blue was the alteration of the catch rates of several Pokémon, itself retained since Blue, whereas Pokémon Crystal featured several notable differences).
6. These games will be released in Japan almost exactly one year after the Japanese release of Pokémon Platinum, being released the day before the anniversary.
7. The font used for the English titles of these games are different than the font that has been used since Pokémon Ruby and Sapphire, while the Japanese logos are still in the same style used since those games. FireRed and LeafGreen also used a different font than the Hoenn games, however, it was still the same color.
8. Additionally, the Ho-Oh crest shaped like a heart and Lugia soul are used in the English logos, while the fire and leaf that appear on FireRed and LeafGreen's Japanese logos were not used in the English release.
9. These games mark the first time that the English versions are announced before the games themselves come out in Japan

Gold receives a redesign while a new player character apparently replaces Kris.
The DS's 3D capabilities are utilized in selecting the starter Pokémon.
The PokéGear has been redesigned. Now, it features two designs, one blue and white for males and another white and pink for females.
Much like Kanto's was for its remakes, Johto's Pokédex has been redesigned. Unlike Kanto's remakes, which contained the same regional Pokédex as the originals, the original regional Pokédex for Johto has been slightly altered, presumably to exclude Kanto-exclusive Pokémon such as Bulbasaur, Charmander, and Squirtle and to include Generation IV evolutions for Johto Pokémon.
An image of certain locations, similar to that of FireRed and LeafGreen, appears when entering the location.
Team Rocket Grunts are designed like they were in FireRed and LeafGreen.
Rocket Executives are also redesigned from Generation II, with four different characters appearing in the games' intro. It is unknown as of yet if they have names.
Ho-Oh and Lugia have their own battle music (they used the standard wild battle music in all Generation II games), while the legendary beasts use a remixed version of their battle theme from Pokémon Crystal.
Kurt and Apricorns make a return to the series along with their respective Poké Balls. Apricorns can now be carried by the player in their own bag with a new item, the Apricorn Case.
Gym Leaders have animated battle sprites, as in Platinum

Elm's Lab has an upstairs level.
Maps have been remade to match the design style used in Diamond, Pearl, and Platinum.
The Battle Tower west of Olivine City, introduced in Pokémon Crystal, returns, bringing with it an entire new Battle Frontier.
A new area to the west of Cianwood City is a Safari Zone.

All 493 Pokémon are capable of following the player similar to Pikachu in Yellow. CoroCoro showed examples of several examples including Steelix and Wobbuffet. Shininess is apparently retained. In battle, like Yellow's Pikachu, they are sent out from the side of the screen, rather than from a Poké Ball.
Similarly to the event Shaymin and Regigigas's effect on Platinum, the Pikachu-colored Pichu to be given to those who have pre-ordered tickets to the twelfth movie will unlock an event near the Ilex Forest Shrine featuring the Notched-ear Pichu.
The Pokémon storage system, bag, party interface and the screen that pops up when pressing the Start or X buttons in the previous games all use the Nintendo DS's touch screen.
Groudon and Kyogre will appear in SoulSilver and HeartGold, respectively, after the Elite Four, and Rayquaza can be caught in both games once the other members of its trio are brought into the game.
Cynthia and Arceus are shown together in a new section of the Ruins of Alph named the Shinto Ruins. This event will allow players to obtain either Dialga, Palkia, or Giratina at level 1.
Eusine, a major character from Pokémon Crystal who was not in the original Gold and Silver, appears, as do other aspects originally featured in Crystal.
A new sidequest, the Pokéthlon, will feature ten mini-games that pit Pokémon in athletic competitions. Its system appears to be analogous to that of Contests from previous games.
Using the Apricorn Shaker, Apricorns can now also be mixed into drinks that increase Pokémon's Pokéthlon stats.
Berries can be grown portably using the Berry Planter, where the Squirtbottle is controlled via the touch screen to water four Berries at a time. It is currently unknown where Berries can be obtained in the first place, but it appears that they do not grow on the trees where their Generation II counterparts were found, as those are used for growing Apricorns.