Pokémon Mystery Dungeon: Rescue Team DX is a revamped, up to date version of the classic Mystery Dungeon games, bringing updated features, new Pokémon, and much more. You play a person who is turned into a Pokémon and must rescue and help your fellow Pokémon while unraveling the mystery of what happened to you. You travel through randomly generated dungeons, recruiting Pokémon, and finishing quests.
Pokémon Mystery Dungeon: Rescue Team DX is a single-player game, and does not have what you would consider to be a traditional multiplayer mode. While you play through the entire campaign alone, you can go into a quest to save a friend who gets stuck in a dungeon. You can also do this for strangers, through the post office in the town.
Head to the post office and then choose “Help a friend” from the options. If you decide to help a friend via the Password option, you will need their password to access the rescue mission. If you pick the Internet option, you will be giving a list of all the available rescue missions and can choose which one you wish to go on.
The bulletin board will show you the Rescue Team that needs help, where they are, the difficulty, the rewards, and how many days are left on that particular rescue mission. You can then load in and track down the team that needs help, then get your reward when you get them out of the dungeon.
So, it’s not multiplayer, but it is a way for the community to interact and engage with each other.