From the back of the case:
"Nintendo Worlds Collide!
Anything can happen in this action-packed fighting game as you square off with tons of characters from Mario to Link to Pikachu, with limitless customization and a wealth of modes, there's no end to the smashing fun!
Weapons and assistants that boggle the mind!
Unleash all-new final smashes!
Solid Snake and Sonic the Hedgehog join the brawl!
Take the fight to distant friends as you brawl with up to four players over Nintendo WFC. You can even send custom-made stages or screenshots to friends.
Exchange friend codes and you can use custom taunts!
Join the Adventure
Challenge events, play stadium and classic modes, or fight through a cinematic adventure! One or two players jump and brawl through enemy-packed side-scrolling levels as they meet Nintendo characters and battle massive bosses."