There are various secret boss fights that you can unlock in Super Street Fighter IV: Arcade Edition.
To fight Akuma, complete Arcade mode without losing any rounds and with a Perfect Victory.
To get Evil Ryu, don't lose any rounds and get a Perfect Victory, before defeating Seth with a Super of Ultra combo finish.
To battle Gouken, don't lose any rounds and get a Perfect Victory, but also you need to have performed ten First Attacks, and have five Super or Ultra combo finishes.
Finally to fight Oni, don't lose any rounds, get a Perfect Victory, perform ten First Attacks and five Super or Ultra combo finishes, and defeat Seth with a Super or Ultra combo finish.
Note: to unlock these secret boss fights, you need to play Arcade mode on the three-round setting.
Added by: MongooseGeneral Jun 30th 2011, ID#7426