In Pokémon Yellow, a new feature was introduced which had your starter Pokémon, Pikachu, follow you around. Pikachu was always behind you and you could always check it to see its happiness. This feature later returned in Amity Square in Diamond, Pearl & Platinum, with a limit to 20 Pokémon. In Heart Gold & Soul Silver, you once again get a partner Pokémon. However, it is not limited to your starter Pokémon.

In Heart Gold & Soul Silver, as soon as you get your Pokémon, Professor Elm will say that your Pokémon can come out and walk along with you. Originally, this would seem to follow the precedent set with Pokémon Yellow, however every single Pokémon can be sent out to follow you. From Bulbasaur to Arceus, you can have any of your favourites follow you. To do this, all it seems you need to do is have the Pokémon at the top of your team and it shall be sent out.

Interaction

Like with Pikachu in Pokémon Yellow, you have the ability to interact with your Pokémon. If you turn around and face your Pokémon, simply press A and you will get to see the mood of your Pokémon. Whether it's happy with you, apathetic or is in trouble due to low health or a status condition. This will allow you to be able to quickly guage how your Pokémon is doing.

In addition to that, there are various Pokémon that have special interactions, with some boosting happiness, depending upon where you are and if it is the right type or species of Pokémon. Many of these interactions you can be notified of by Lyra/Ethan when you call them in the specific area, but there are a fair few that even they do not know of. Below is a table of the Pokémon, the interactions and the locations for many of them. Some interactions may seem to be repeat

Interaction Table
Location Pokémon Interactions
Route 29 CHIKORITA is waving its leaf around.
CHIKORITA is making its leaf twitch.
Route 30 TOTODILE is moving its jaw.
TOTODILE is opening and closing its mouth.
Route 31 CYNDAQUIL blew out a couple of fireballs.
CYNDAQUIL blew out a fireball..
Dark Cave Ice Types Pokémon is cheerful that it’s become a bit cold!
Sprout Tower BELLSPROUT swayed and danced around as it pleased.
BELLSPROUT swayed around, dancing in a strange manner.
Ruins of Alph A strange sound is coming from UNOWN...
UNOWN started spinning around in circles.
UNOWN is growling in a way that sounds almost like speech...
Your Pokémon isn’t moving.
Your Pokémon seems to be singing something?
Sinjoh Ruins ARCEUS looked up at the sky and shouted loudly!
DIALGA gathered itself up and let out a huge roar!
PALKIA’s body shook with a great roar!
Route 33


Grass Type
Water Type
Fire/Rock Type
Chikorita/Bayleef/Meganium is dancing and splashing around!
Cyndaquil/Quilava/Typhlosion seems to be very surprised that it’s raining!
Totodile is looking up with its mouth gaping open.
Croconaw/Feraligatr is looking up with its mouth wide open.
Grass Pokémon is very happy about the rain!
Water Pokémon seems to be happy about the rain!
Fire/Rock Pokémon is making an unhappy face....
Azalea Town Fire Types Your Pokémon is hot and cheerful!
Azalea Town Gym SPINARAK/ARIADOS began to scuttle around!
Slowpoke Well
Fire Type
Water Type
Your Pokémon seems somehow unhappy. (During TeamRocket Takeover)
SLOWPOKE/SLOWBRO seems very happy!
Your Pokémon doesn’t like splashing around on the ground...
Fire Pokémon seems very unhappy to be wet...
Water Pokémon seems very happy and is jumping around!
Ilex Forest FARFETCH'D is dancing around happily!
FARFETCH'D is happily waving ITEM around and singing.
CELEBI danced happily!
CELEBI danced beautifully!
HERACROSS is clinging to the tree!
SHROOMISH sent a ring-shaped cloud of spores into the air!<
Route 36 SUDOWOODO is staying completely still--imitating a tree!
Goldenrod City Gym CLEFAIRY is very happy!
CLEFAIRY is waggling a finger and dancing!
Goldenrod Radio Tower Electric Type
Ghost Type
Electric Pokémon seems to be getting an electrifying feeling!
Your Pokémon is feeling alert because of something...
National Park Bug Type Bug Pokémon is a little excited
Ecruteak City Dance Hall PICHU danced along with the Kimono Girls!
BELLOSSOM danced better than the Kimono Girls!
MIME JR. is dancing in the same manner as the Kimono Girls.
Burned Tower Pokémon shook the tower with its voice!
Pokémon howled loudly!
Bell Tower HO-OH is looking to the sky and shouting!
HO-OH shook the tower with its cry!
Route 39 TAUROS suddenly roared!
MILTANK seems to be very happy!
MILTANK is so happy, it started rolling around.
Lighthouse AMPHAROS sparkled in concert with Amphy!
Cianwood City KRABBY moved sideways!
Route 40 POLIWAG swung its belly around.
Whirl Islands
Water Type
POLIWAG swung its belly around.
LUGIA moved its long body and let out a great big roar!
Water Pokémon  seems happy to be all wet!
Route 42 Rock-Type Pokémon is looking at the mountain as if anticipating climbing it.
Route 47
Flying Type
...Oh? DITTO’s appearance... Didn’t change!
Flying Pokémon is flying through the sky with grace!
Embedded Tower
MEGANIUM turned its head and let out a fighting yell!
TYPHLOSION emitted fire and shouted!
FERALIGATR is swinging its arms around and shouting!
KYOGRE opened its mouth wide and howled!
GROUDON stuck out its claws and ROOOOAAARRRED!
RAYQUAZA moved its long body and let out a great big roar!
Lake of Rage
Grass Type
Water Type
Fire/Rock Type
MAGIKARP is leaping around more than usual!
GYARADOS howled very loudly!
Grass Pokémon is very happy about the rain!
Water Pokémon seems to be happy about the rain!
Fire/Rock Pokémon is making an unhappy face...
Rocket Hideout ELECTRODE is trembling!
Ice Path
Ice Type
Grass Type
Whoa! A cold wind suddenly blew! And now it looks happy?
Ice Pokémon is cheerful because of the cold!
Ice Pokémon is cheering happily because of the cold!
Ice Pokémon just looks so very happy!
Grass Pokémon seems unhappy about the cold...
Grass Pokémon made its body slightly smaller because of the cold...
Mahogany Town Gym Ice Type
Grass Type
Ice Pokémon is cheerful because of the cold!
Ice Pokémon is cheering happily because of the cold!
Ice Pokémon just looks so very happy!
Grass Pokémon seems unhappy about the cold...
Grass Pokémon made its body slightly smaller because of the cold...
Dragon's Den Dragon Type Pokémon suddenly barked!
Pokémon looks excited!
Pokémon suddenly howled!
Pokémon is staring into Character's eyes.
Pokémon is growling softly.
Victory Road MEGANIUM turned its head and let out a fighting yell!
TYPHLOSION emitted fire and shouted!
FERALIGATR is swinging its arms around and shouting!
Route 1 BULBASAUR wiggled its vine!
BULBASAUR snapped its vine!
Route 2 CHARMANDER flared its fiery tail!
Viridian Forest
PICHU/PIKACHU/RAICHU danced around very happily!
HERACROSS is clinging to the tree!
SHROOMISH sent a ring-shaped cloud of spores into the air!
Route 3 SQUIRTLE fell down and got a little frustrated!
Mt. Moon CLEFFA/CLEFAIRY/CLEFABLE is looking up at the sky.
CLEFFA/CLEFAIRY/CLEFABLE suddenly started dancing!
Cerulean City Gym TOGEPI suddenly began crying softly!
MAGIKARP is jumping energetically!
Cerulean Cave Mewtwo/Mew suddenly shouted!
Mewtwo/Mew looked up at the ceiling and howled!
MEWTWO slapped at the ground!
MEW suddenly started spinning around!
Power Plant PICHU/PIKACHU/RAICHU seems to be very happy!
PICHU/PIKACHU/RAICHU had fun dancing a dance!
PICHU/PIKACHU/RAICHU is so happy, it began to dance!
PICHU/PIKACHU/RAICHU is so happy, it started dancing!
Rock Tunnel
Rock Type
ONIX is happily digging in the ground!
STEELIX is happily digging itself into the ground!
Pokémon is having fun rolling around!
Pokémon started grinding at the rocks!
Pokémon is having fun hitting rocks together!
Pokémon started pounding the ground flat!
Diglett's Cave Your Pokémon stretched out its body and is relaxing.
DIGLETT/DUGTRIO seems very happy!
Saffron City - Copycat's House MIME JR. mimicked GOLD
Saffron City - Mr. Psychic's House Psychic Types ...... ...... ...... ...... ...... ...... ...... ...... ...... ...... ...... Pokémon silently nodded!
Silph Co. - Rotom Room
ROTOM is happily zapping and jumping in circles!
ROTOM is having fun dancing a lively jig!
Celadon City PORYGON stammered something...
Celadon City Gym
Water/Grass Type
Fire Type
TANGELA is extending its vines and wrapping itself in them! Seems like fun!
Water/Grass Pokémon seems happy to have taken a shower!
Fire Pokémon seems unhappy to have taken a shower...
Lavender Town Ghost Types Pokémon is having fun swaying back and forth.
Fuchsia City TAUROS started breathing roughly through its nose in excitement!
Seafoam Islands Ice Type
Grass Type
Ice Pokémon is cheerful because of the cold!
Ice Pokémon is cheering happily because of the cold!
Ice Pokémon just looks so very happy!
Grass Pokémon seems unhappy about the cold...
Grass Pokémon made its body slightly smaller because of the cold...
Mt. Silver CHARIZARD blew out a plume of fire and looked eager!
PIKACHU is trembling with eagerness!
SNORLAX is feeling very eager
Items

As with when you take your Pokémon out for a stroll in Amity Square in Diamond, Pearl & Platinum, when you are out with your Pokémon in this game, your Pokémon will sometimes find items. These items include Berries and Accessories for your Pokémon. The items that they get are dependant upon their location and are as follows;

Picture Accessory Name Location
Big Leaf
おおきいはっぱ
Route 6
Big Scale
おおきいウロコ
Routes 27 & 48, Olivine City
Black Beard
くろいひげ
Sprout Tower
Black Fluff
くろいわたげ
Route 42, Dark Cave
Black Moustache
くろいひげ
Sprout Tower, Bell Tower, Dragon's Den
Black Pebble
まっくろストーン
Union Cave, Dark Cave, Rock Tunnel, Cerulean Cave
Blue Feather
あおいはね
Route 37
Blue Flower
あおいはな
Route 11
Blue Scale
あおいウロコ
Routes 14, 20 & 41, Mahogany Town, Lake of Rage
Brown Fluff
ちゃいろのわたげ
Route 39
Determination
にじみでるきあい
Ruins of Alph, Mahogany Town Rocket Hideout
Eerie Thing
ぶきみなもの
Ruins of Alph, Victory Road
Glitter Boulder
きらきらストーン
Route 24
Glitter Powder
キラキラパウダー
Power Plant
Green Scale
みどりのウロコ
Route 34
Jagged Boulder
ごつごつストーン
Mt. Silver Outside, Diglett's Cave, Rock Mountain
Mini Pebble
ちびストーン
Routes 10 & 26
Mystic Fire
ふしぎなほのお
Burnt Tower, Shining Lighthouse
Narrow Leaf
ほそいはっぱ
Route 7
Narrow Scale
ほそいウロコ
Routes 2 & 12, Lake of Rage
Orange Flower
オレンジのはな
Route 43, Ecruteak City
Orange Fluff
オレンジのわたげ
Routes 15 & 36
Peculiar Spoon
ふしぎなスプーン
Goldenrod City Radio Tower
Pink Flower
ピンクのはな
Route 30
Pink Fluff
ピンクのわたげ
Routes 16 & 33
Pink Scale
ピンクのウロコ
Routes 13 & 40, Cerulean City
Poison Extract
どくエキス
Ruins of Alph, Mahogany Town Rocket Hideout, Cerulean Cave
Pretty Dewdrop
きれいなしずく
Dragon's Den, Mt. Silver, Viridian Forest
Puffy Smoke
モコモコけむり
Burnt Tower, Bell Tower
Purple Scale
むらさきのウロコ
Route 47, Lake of Rage
Red Feather
あかいはね
Route 38
Red Flower
あかいはな
Route 35, Ecruteak City
Round Pebble
まんまるストーン
Route 10, Mt. Moon
Seashell
かいのかけら
Whirl Islands
Shed Claw
つめのカラ
Whirl Islands, Mt. Silver
Shed Horn
つののカラ
Whirl Islands, Mt. Silver
Shimmering Fire
メラメラほのお
Burnt Tower, Shining Lighthouse
Shiny Powder
ピカピカパウダー
Radio Tower, Mt. Moon
Small Leaf
ちいさいはっぱ
Routes 5 & 8
Snaggy Pebble
こつこつストーン
Mt. Silver Outside, Diglett's Cave
Snow Crystal
ゆきのけっしょう
Ice Path, Mt. Silver
Sparks
パチパチひばな
Shining Lighthouse
Spring
バネ
Goldenrod City Radio Tower
Stump
きりかぶ
Ilex Forest, Viridian Forest
Thick Mushroom
ふといキノコ
Ilex Forest, Viridian Forest
Thin Mushroom
ほそいキノコ
Ilex Forest
Wealthy Coin
おかねもちコイン
SS Aqua
White Beard
しろいひげ
Sprout Tower
White Feather
しろいはね
Route 3
White Flower
しろいはな
Routes 9 & 32
White Fluff
しろいわたげ
Route 31
White Moustache
しろいひげ
Bell Tower, Dragon's Den
Yellow Feather
きいろのはね
Route 3
Yellow Flower
きいろのはな
Route 1, Ecruteak City, Viridian City, Pewter City, Cerulean City, Vermillion City, Celadon City, Lavender Town, Fuchsia City
Yellow Fluff
きいろのわたげ
Route 2

 
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