Successfully complete the indicated task to unlock the corresponding bass:
  Beach Life: Successfully complete Co-op mode on the Hard difficulty setting.
  Neversoft Skateboard: Successfully complete Co-Op mode on the Expert 
  difficulty setting with a "Five Star" rank on all songs.
  PendulAxe: Successfully complete Co-op mode on the Expert difficulty setting.
  Tiki Fortune 4: Successfully complete Co-op mode on the Easy difficulty 
  setting.