If it was a big deal when Nintendo announced that Super Smash Bros Brawl would include a single player mode, then this is like icing on the cake. The previously-announced Subspace Emissary mode will also be playable cooperatively.
While player one will act as the main protagonist of the adventure, dictating the storyline and being the focus of the action, a second player will be able to join in the effort as a sort of sidekick, handling the light work. The scope of the camera will not adjust to accomodate both characters, but will instead remain fixed on the protagonist. If the second player can’t keep up, he or she will "space jump" back into view. Getting knocked off screen, of course, loses a life.
The Subspace Emissary mode has really begun to sound like a fully-developed portion of Super Smash Bros Brawl, and not the tacked-on addendum to the real meat of the game that many had once expected. Good show, Nintendo.
