Built near Indigo Plateau, the final destination for many Pokémon Trainers, the Trainer House provides a place for Trainers to battle in a controlled environment. According to visitors on the first floor of the building, the best Trainers gather here. These Trainers turn out to be real-life friends of the player, whose own parties are submitted to the game through Mystery GiftGSC or the PokéwalkerHGSS.
In the Generation II games, the player may only battle once per day and if the opponent has a Pokémon that the player has not seen before, the Pokémon will be added to the Pokédex.
The Trainer in the basement will be the last person who the player used Mystery Gift with, with their team being whatever Pokémon (excluding held items, gender and stats) were in the other person's party at the time. If the player has never used Mystery Gift with anyone, the Trainer will be Cal, using the following team:
In Pokémon HeartGold and SoulSilver, the player will initially find only Ace TrainerCal in the basement of the Trainer House. When the player connects their Pokéwalker with another person's and then resyncs it back to their game, the other Trainer and their Pokémon will appear in the basement of the Trainer House. A maximum of ten additional Trainers besides Cal may be gathered in this way.
Other Trainers' teams will consist of whatever Pokémon (including held items) were in their party when they sent their Pokémon to the Pokéwalker, with the level of Pokémon capped at level 50. After a battle, all Pokémon will be restored to full health and held items restored. Players will earn no experience or money, but they will receive 1 Battle Point for winning. If an opponent has a Pokémon that the player has not seen before, the Pokémon will not be added to the Pokédex.
Through the use of two Pokéwalkers, connected to the player's game and a friend's, the player can battle themself by connecting the Pokéwalkers and receiving a gift from the friend's Pokéwalker.