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.

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.

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. It is unknown if there's just a set list for the Pokémon to get or if each Pokémon has a unique list of obtainable accessories.