List of Mario & Luigi: Dream Team glitches
This is a list of glitches in the game Mario & Luigi: Dream Team.
NOTE: Unless otherwise noted, all names are conjectural.
Freezing occurs in the game on certain occasions, but mainly toward the end of the game in Neo-Bowser Castle, where the Mario and Luigi find themselves at idle animations and not being able to do anything. This appears in all original versions of the game, but a patch was released on September 5, 2013 fixing many of these issues.
Antasma X glitch
Corrupted Save File
It is possible that the game will display a black screen with a message saying that the save data has been corrupted when the player loads it up. This will force them to start the whole game over from the beginning. Something similar also happens when selecting a new save file, after selecting a file, the screen goes black and freezes, taking the player to the Home Menu. These instances of save file corruption seem to only happen on the digital version.
The player should be in Neo Bowser Castle and in any area with the bombs. They must do the same thing as the "Non-bomb panic" glitch explained below, though they should time it differently. This should result in Mario bouncing first, followed by Luigi (bouncing in the air); however, there is a 1% chance of this outcome occurring.
Luigi standing on lava
The player needs to go to Neo Bowser Castle in the sections with the moving, fire breathing Bowser statues. If the player uses the Side Drill move in the area where the Bros. Ball is needed and cross the moving statues, Mario will land on the platform, but Luigi will land in the lava and stand there without jumping out. Also, the player can hit a Kamek Block and immediately fall into the lava. This results in both Mario and Luigi standing on the lava until the cutscene where the path is shown on the map ends, then Mario and Luigi will bounce out of the lava.
The player should be in Neo Bowser Castle, in any area with the bombs. When the bomb comes to Mario and Luigi, hammer Mario by pressing (press first until it shows the hammer icon). It should sometimes freeze the bomb, or explode. But Mario and Luigi won't panic for the explosion and warp.
When visiting Dozing Sands for the first time, the player can skip all of the activity involved in retrieving the Dozites needed to access the area where Torkscrew is fought. In the area where the badge shop is, Mario and Luigi need to lure a Sandoon to the dark gray high ledge in the east, and while touching the wall, both brothers must jump on it to initiate a battle. The player must then flee from the battle, hold and repeatedly press the Buttons. If done correctly, Mario and Luigi will do another jump in the air and over the high ledge. This is a frame perfect trick, so it might take a while. Currently, this sequence break works in all versions of the game. 
Out of Bounds
Luigi under The ground
Out of bounds in Mushrise Park
In Mushrise Park, there's a bridge near a Brock and some Mushroom style platforms in an area to the right. If Mario and Luigi go under this bridge and jump towards a tree at the north end of the area at the right angle, they can then end up getting inside said object and eventually walking past the invisible wall at the edge of the park to the vast empty void beyond. 
This can lead the duo falling into the Mini Mario only area and getting permanently stuck there with no way to leave (saving here will render the save file unusable); the Bros. can get separated with Mario on top of the bridge and Luigi under it, also potentially destroying the save file; the Bros. wandering off the edge of the park, causing the screen to stay locked in one area while the map below shows them wandering all over the outskirts of the park and it can also cause Luigi to fall off the wall while Mario stays on top of it, leading to both characters getting pulled inside solid ground.
Standing on water
Mini Mario is required. The player needs to go to Driftwood Shore and then go to the cave after they talked to Broque Madame at Rose Broquet. They will earn an old lithograph. After they went to the door, they will enter the cave. On a spot, they have to hold to the left on the for 1 minute. After that, they have to hold the right button on the . If done correctly, Mario will stand out of bounds, and if the player holds to the right on the some more, Mario and Luigi will walk on the water.
Broken motion controls glitch
In some points in the game involving gyroscope controls, sometimes the game can stop registering any gyro movement altogether. This can cause battles where this happens to become impossible to win because it is impossible to avoid sustaining damage. This is most likely to occur in the Zeekeeper battle with Giant Luigi in Somnom Woods, and in the "Repel the Shell" portion of the Giant Bowser battle. During the Zeekeeper battle, the game is slow or inaccurate at registering all motion controls, which makes it extremely hard if not impossible to dodge attacks, and in the Giant Bowser Battle, the game will only register minor motions from the 3DS, while larger motions will magnetically pull Luigi towards the lava. However, there are still cases where the 3DS can literally be held upside-down, and Luigi will not budge an inch. In both battles, the game will occasionally default Luigi to the bottom left corner of the screen, which, in the Giant Bowser battle, will cause him to continuously fall into the lava until he runs out of health. It is believed that this is because these gyroscope portions are preceded by a portion of character dialogue, and the game may forget to re-activate the gyroscope afterwards. This has now been fixed by a 3DS update, although it still can work.
Mini Mario's solo adventure
With the Mushrise Park sequence break, the player can also trap Luigi in the Mini Mario only area, and have Mario adventure alone through Pi'illo Island. This glitch leads to gameplay changes and side effects such as, Mario being able to enter any area on the island (that's reachable without special moves like Ball Hop), and have Luigi stuck in the middle of nowhere on the map. He can also do things like buy items from shops, hit switches and solve certain puzzles, talk to NPCs and various other things. However, there are some side effects: if the player attempts to battle an enemy the game will freeze with no music unless they jump on the enemy or get out of Mini Mario (see below), entering cutscenes that would involve Luigi will freeze the game, Pipes and Drill Digger do not work; using elevators, lifts or certain other things freeze the game and talking to Kylie Koopa freezes the game. The player can return Mario to normal size by walking to a Dreampoint or the Battle Arena but declining to enter, or by jumping on an enemy. If the player attempts to battle an enemy without Luigi AFTER returning to normal size, the battle goes just fine, except there is a No Bros. Move rule for obvious reasons.
To get Luigi back, the player should do the Mushrise Park glitch again, but go south. Mario and Luigi will fly in as if flung from a Slingshroom. It also seems as though there's another way to get Luigi back: Jump off of Mount Pajamaja and enter a new room, and Luigi should reappear.
No demo sign
The player needs to go to the Menu and then press Guide, then press Attacks. The demo sign appears in a little while after they scrolled down then scrolled back up quickly. If done correctly, they will have no demo signs while selecting the attack. When they press the button, it can start the demo even though the sign is not here.
Luigi's missing half
If the player tries to Ball Hop directly under the first Attack Piece Block encountered chronologically in Somnom Woods, Luigi will collect the Attack Piece, but will be missing his lower half until the player moves again.