How do I know when I'll fight Akuma/Gouken at the end of Arcade mode?

Solution 1:

There are actually 4 secret bosses (in SSFIV AE and USFIV). Assuming you have selected Arade mode with 1 round per game you need to meet the following requirements to be able to fight them:

• Akuma
  • No Continues
  • 1 Perfect
• Evil Ryu
  • No Continues
  • 1 Perfect
  • defeat Seth with Super/Ultra
• Gouken
  • No Continues
  • 1 Perfect
  • 5 First Strikes
  • 3 x Super/Ultra Finishes
• Oni
  • No Continues
  • 1 Perfect
  • 5 First Strikes
  • 3 x Super/Ultra Finishes
  • defeat Seth with Super/Ultra

These requirements increase once you choose multiple rounds per game.

You can only fight the boss if he is a member of the cast for your game. This means you cannot fight Oni or Evil Ryu in Street Fighter IV or Super Street Fighter IV. Here is a list of all bosses in the different versions:

• Street Fighter 4: Akuma, Gouken
• Super Street Fighter 4: Akuma, Gouken
• Super Street Fighter 4 Arcade Edition (201X): Akuma, Gouken, Evil Ryu, Oni
• Ultra Street Fighter 4: Akuma, Gouken, Evil Ryu, Oni

TIP: You can use the second controller as a last resort. If you miss your Super/Ultra on Seth you can press Start and you will enter a 2 player game. Once you win you can resume Arcade mode and fight against Seth again. This is not counted as a loss.

Source: http://www.xboxachievements.com/forum/showthread.php?t=314180