Pokémon Let's Go Pikachu and Let's Go Eevee have a new feature of co-operative play. As the game can be played with one Joy-Con, another player can pick up a Joy-Con and join the game as another trainer on the quest. This turns battles into 2 VS 1 battles and has both players able to throw balls to capture a Pokémon.
When playing in Co-Op mode, there are various restrictions. First, the second player cannot interact with any NPC, Item or wild Pokémon and the players can walk through eachother. The Pokémon following the trainer will always be the 2nd Pokémon in the party. With this, the second player cannot ride a Pokémon while the other player can.