Tag Mode is one of several multiplayer modes available in Dragon Quest IX. It is the 'passive' wireless mode which uses the DS wireless capabilities while it is in sleep mode. It is used to exchange player data and items with other Dragon Quest IX games, including treasure maps.
Tag Mode is one of the major reasons Dragon Quest IX was extremely popular in Japan. It was the source of a new Guiness World Record for most game players communicating anonymously in a multiplayer mode.
Before going into Tag Mode, the player is able to select a phrase which his/her Hero will greet other Dragon Quest IX games with, as well as a special item to give to those players as well.
When the game encounters another DS using Dragon Quest IX in Tag Mode, the 2 games exchange data. Each of the heroes appears in the Quester's Rest where they wait to be greeted as a guest by the player. These 'clone' characters will then help to expand the Quester's Rest until they are later dismissed by the player.
Dragon Quest Monsters: Joker 2
In Dragon Quest Monsters: Joker 2 you can enter Tag-Mode to battle other monsters and teams. However, there is also a special feature: If you are in Tag-Mode near a person canvassing for guests in Dragon Quest IX you can battle and scout a rare monster from that game!
Treasure maps are by far the most sought after item in Tag Mode. Since treasure maps are randomly generated from out of 8 million possible layouts, finding rare and rewarding ones with great treasures or monsters that yield high experience values is hard to come by. As a result, good maps are extremely popular items to be traded while in Tag Mode. One particular map, known by fans as Masayuki's Map in honor of the person who discovered it, had a dungeon whose 15th floor was exclusively populated by Metal King Slimes; it became so popular that it was shared across much of Japan. A similar map called the Kawasaki Locker was similarly renowned for its mixture of incredibly difficult monsters and chests which contained some of the game's rarest equipment.
Tag Mode has been critized by North American and European fans as it uses local DS wireless only, rather than wifi internet. As Japan is a much more densely populated country where the Dragon Quest series is very popular, finding other players using Tag Mode is quite common. It is debateable whether the Tag Mode feature will be nearly as successful outside of Japan where the series is not as popular and the population much more spread out. This had led fans to question why wifi was not included in the worldwide release in a form similar to the Global Trade Center in Pokémon games.