Pokémon Pokopia lets a player invite up to three other players to visit.
This means a session can include the host plus three visitors. The visitors can spend time in the developed Pokémon space, and each invited player can bring one Pokémon along, adding a cooperative and social dimension to the town-building experience.
The game supports both local wireless and online play. Nintendo's promotional material also describes GameShare, which can allow a friend who does not own the game to join a compatible session under the stated system and service requirements.
The number three refers specifically to additional visitors, not the total number of people in the session. That distinction matters when reading multiplayer descriptions, because “three other players” means the host is not included in the count.