Select 'Battle' then 'Training'.
Select any characters for yourself and your opponent. In the match press Start and RB twice to go to 'Standby Settings'. From here change Standby to 'On' and exit out. Now wait for about 15 seconds and a message saying 'A Battle of Destiny' will appear on screen.
You will now be in a ranked match against a random opponent and win or lose you will also unlock: