Unlock Dark Characters
     You  Can  do  this  in the arcade mode and not necesary you don't 
have  to lose and use a continue to have them. When you win, a message 
will  appear.  They  aren't  different  except Galford that is without 
Poppy and his special.

Dark Galford (Or without Poppy His Dog): 
     Win 6 times with different characters

Dark Nakoruru:
     Win 3 times with different characters