Pokémon HeartGold and SoulSilver

Pokémon HeartGold and Pokémon SoulSilver are Generation IV's remakes of the original Generation II games, Pokémon Gold and Silver. Nintendo released Pokémon HeartGold and Pokémon SoulSilver versions in Japan on September 12, 2009. The games were released on March 14, 2010 for North America and March 26, 2010 in Europe.

These remakes incorporate the many advancements that the series has undergone since Generation II, much like how FireRed and LeafGreen changed from Red and Blue.

Blurb
Prepare for thrilling new adventures as Legendary Pokémon awaken!

'''Explore the Johto region as you catch, train, and battle with your favourite Pokémon by your side. Reach for the sky—call forth the Legendary Pokémon!'''

Enjoy minigames with your trainer Pokémon!

Travel with your favourite Pokémon!

Changes from Gold, Silver and Crystal

 * The new female character named Lyra was added in HeartGold and SoulSilver and she replaces Kris (the female protagonist from Crystal), and Gold has been renamed as Ethan.
 * You receive the Vs. Recorder early in the game by Ethan or Lyra, depending on the gender you chose.
 * You have to visit the Sprout Tower and complete the task in it in order to access the Violet City's gym.
 * The Global Terminal is found at Goldenrod City.
 * All 493 Pokémon can follow you, including the Shiny Pokémon, and you cannot turn off the feature. To do this, you must put the Pokémon at the first in your party (the lead Pokémon), then it will appear behind you. You may also interact with it to show how it feels right now.
 * All the gyms are appeared to be tougher than in the original Generation II games.
 * The tiles of the puzzle in Ruins of Alph can be rotated to solve the puzzle. player characters who succeeded solving the Kabuto puzzle will receive an Unown Dex from a man in the ruins.
 * Team Rocket now have four executives - Proton, Petrel, Ariana, and Archer.
 * Eusine (from Pokémon Crystal) returns, he is a character who is interested in Suicune. The player character will meet him when the player character found Suicune. His appearance also can be found at the intro video, which is a man wearing purple clothes. He will be seen whenever the character will encounter Suicune.
 * Additional routes, Route 47 and Route 48 is placed next to Cianwood City. A Safari Zone can be found at Route 48, owned by Baoba.
 * The areas in the Safari Zone can be altered after you receive the second challenge Baoba gives you.
 * Just like in the original Gold, Silver, and Crystal, there are many day based activities like the Bug Catching Contest, Goldenrod to Saffron City train, Olivine to Vermilion City ship, etc. These are also on the days they were in the originals too.
 * Next to the National Park there is the Pokéathlon Dome in which you can compete in minigames to win medals, which is open after you receive the Plain Badge.
 * The move Flash is now a TM move.
 * Hills that required HM08 Rock Climb can now be found.
 * Some trainers in Kanto region have Generation III and IV Pokémon.
 * The Battle Frontier at Route 40 replaces the Battle Tower.
 * The Pal Park replaces the Kanto Safari Zone in Fuchsia City.
 * There is Viridian Forest in Pokémon HeartGold and SoulSilver, which the earlier versions do not have (Pokémon Gold, Silver, Crystal), though the earlier games had a forest but with no Pokémon in it.
 * The radio functions in the PokéGear have been altered, which the player character can manually tune the channel to listen or pressing one of the four buttons to gain immediate access to the channels available.
 * Some channels have to be manually tuned, and must be standing in a specific location.
 * Poké Flute - Must be in the Kanto region, tune manually to the upper middle section. This radio channel helps to wake up the Snorlax in Route 11.
 * Mysterious Transmission - Inside the chamber of Ruins of Alph, manually tune the music to the center. It produces a strange sound, which is produced by Unown. It helps to increase the chance of meeting a rare-shaped Unown.
 * Giovanni returns in the remake, since he didn't return in the original Generation II games and he only appears in the Celebi event.
 * Silver's past was revealed in the remake that explains that he's the true son of Giovanni.
 * Brock, Sabrina, and Blaine were wearing completely different clothes.
 * Lyra's dialogue was included in the story if she's a non-playable character, unlike Kris and Leaf didn't appear in the story as non-playable characters in the previous games.
 * The Sinnoh Gym Leaders and Cynthia appear as Minor Characters in the remake.
 * Red uses a Lapras instead of an Espeon when the player character challenges Red.
 * After beating Red, Prof. Oak will give the player character any one of the Kanto starters while Steven will give any one of the Hoenn starters.

PokéWalker

 * The Poké Walker is a handheld pedometer that resembles a Poké Ball. It was sold with the HeartGold and SoulSilver Pokémon games.
 * The Poké Walker can connect to HeartGold and SoulSilver cartridges via infrared signals and can "hold" one Pokémon that you then carry around with you.
 * A Pokémon being carried around in this manner will receive experience points and closeness, as well as the player character gaining "watts", an in-game currency that can be used to find and catch wild Pokémon, search for items, and unlock new locations within the Poké Walker.
 * Up to three Pokémon can be captured and stored on the Pokewalker, but only one will appear on the inventory screen.
 * You will also be able to receive items through other Poké Walker devices using infrared.
 * The Poké Walker is similar to the Pokémon Pikachu 2 pedometer/virtual pet in its use of Watts as currency to trade for items.

Trivia

 * Fish or sea Pokémon can follow the player character on land, although they have to live in water.
 * Most legendary Pokémon or large Pokémon cannot follow the player character when the player character enters a building.
 * Lyra appeared in the anime in a 5-episode arc to promote HGSS.
 * In both versions you get to fight both Red and Blue (from FireRed and LeafGreen versions).
 * Wailord can walk with you outdoors but is in its Poke Ball when indoors.
 * Lyra/Ethan is revealed to be the Day-Care Checker's granddaughter/grandson.