Its pretty straight forward.
1. Go offline mode
2. Ghost battle
When you are doing this game mode you just keep fighting enemies even if you lose until you give up. Taking on a tag team represents 2 ghosts being beat and a single is well 1 counted as defeated. It doesn't have to be in a row either
Apparantly people are reporting you can play a few games of ghost battle then go to arcade and it unlocks with "solo warrior" achievement.