One day, the people from the Mushroom Kingdom receive an invitation to visit Pi’illo Island, turned into a touristic region. As they visit the castle, Mario and Luigi stumble into an ancient artifact looking like a stone pillow. As Luigi falls asleep on it, a dark character appears and kidnaps Princess Peach and take her inside Luigi’s Dream.
Mario & Luigi: Dream Team plays roughly like the previous Mario & Luigi RPG games. The player controls both Mario and Luigi at the same time, using the A button to make Mario perform various actions and the B button to make Luigi perform similar actions. The battles are turn-based and also use the A and B button to control Mario and Luigi. Pressing the buttons at the right moment allows the brothers to make extra attacks, deal extra damage, and evade or counter enemy attacks. When a battle is over, the brothers gain experience and eventually level-up. As they do, their stats rise and the player can choose a stat to rise even more by using a slot-machine like system. At certain levels, they change ranks (from Mushroom to Shell rank, from Shell to Flower rank and so on). When changing ranks, the player can choose one bonus (such as an extra equipment slot, higher HP, etc.) from a list.
The game is split between the Real World and the Dream World, both having gameplay differences. The Real World has a top-down view and both Luigi and Mario fight in battle, while the Dream World has a side-scrolling view and, since the Dream World is inside Luigi’s dreams, Luigi himself is repalced by his dream alter-ego, Dreamy Luigi. Dreamy Luigi has the same basic controls as Luigi, but he can sometimes merge with the Dream World to help Mario solve puzzles and reach certain areas. Such actions are called ‘Luigination’ or ‘Luginary Skills’ and use the touch screen to interact with the Real World Luigi, causing changes in the Dream World. In battle, Mario fights alone, with Dreamy Luigi merging with him to give him higher stats. When Mario Jumps on an enemy, for instance, Dreamy Luigi will also jump on the enemies. Like in the other Mario & Luigi RPG games, special attacks called Bros. attacks can be used to deal heavy damage by using both brother’s skills. In the Dream World, the Bros. Attacks are replaced with Luiginary Attacks. These use Dreamy Luigi clones called Luiginoids.
There are special giant boss battles that play holding the 3DS sideways like a book and using the stylus to attack, evade and counter. In these fights, Dreamy Luigi gets bigger and fights the foe with Mario helping him.
Various items and equipment can be found all over the map, with some, like beans and rescued Pi’illo folks, having a menu to show how many have been found. The collection menu also has an ‘Expert Challenge’ menu, showing points-awarding goals to achieve in battle. Completing these challenges awards equipment pieces.