Dragon Quest Builders 2 does feature online multiplayer. You can play with up to three other players in your created worlds or theirs, but it is gated behind some content in the game and not accessible from the very beginning. To play with friends in multiplayer you will need to have completed the Furrowfield Island adventure and then head back to the Isle of Awakening.
Accessing multiplayer is done through a location on the island known as “The Teleportal.” You will be granted access to the teleportal after returning to the island after the first big quest. It is a fast travel location so you can go there anytime when on the Isle of Awakening.
Once at the teleportal you can select a number of different options when it comes to multiplayer. You can choose to invite visitors to your island or visit other player’s islands. When inviting players to your islands you have the ability to allow friends of friends, limit the number of players, and the ability to tweak a number of settings from allowing chest access, building, explosions and other things from the visiting players. If you’re visiting someone else’s island you’ll be bound by the rules that they set when creating the invitation.
Once you set your rules you will launch into an online version of your island and players can join you automatically depending on the settings you’ve chosen. To leave the multiplayer version of your island you must head back to the teleportal.
