Co-op mode
Co-op mode is a mode where the player can get another player to help him or her with 1-Player modes over Wifi or directly.
Wi-Fi
Over online play, one can get other players to help with the Home-Run Contest game mode and the Multi-Man Brawl game mode.
Local
You can get a friend to help you with The Subspace Emissary, All-Star Mode, Boss Battles, Target Smash, Home-Run Contest, or Multi-Man Brawl.
Subspace Emissary
The character allowance stays the same, but the first player gets three characters (five in the Great Maze) and the second player gets one, rather than one player getting all of them. The second player can make things easier or harder depending on the stage the players are on. If they are on a stage that has lots of enemies, this can help because there are twice the number of people that help to defeat the enemies and one more person that enemies can gang up on. But on other stages, such as stages with a boss, the second player can be a burden. For example, if Tabuu uses his Off Waves attack, both players may be KO'd, thus costing the players two characters rather than only one. Note that the second player can join at any time by pressing the start or + button.
All-Star Mode
If two players attempt to do All Star Mode, they will go though the normal format with a few minor changes:
- The final character fought—Olimar—now has a second Olimar to help him out.
- If one player is KO'd, the other player cannot continue on his own; it is as if both players had been defeated.
- Instead of having three Heart Containers, the players now have five, with the two extras appearing below the platforms that hold the original three.
- At the end of the event, you get a combined two-player score instead of two scores to be recorded onto both characters. However, you receive both trophies.
Boss Battles
Co-op Boss Battles has a format very similar to that of 1-player Boss Battles, with a few of the same slight differences that All-Star mode has:
- If one player is KO'd, the other may not carry on by his or herself.
- There are five heart containers.
- There is only one final score rather than two to be recorded onto the characters.
Target Smash, Home-Run Contest, and Multi-Man Brawl
Target Smash, Multi-Man Brawl and Home-Run Contest follow the same format as in one-player mode, except for the fact that there are two people playing rather than one. Challenges for these can be broken in two-player; in fact, it is probably easier to break challenges in co-op mode.