Capcom Fighting Collection

To fight any characters extra battle you need to win 3 of the first 5 fights with an EX move or in DARK FORCE.
The easiest way to get this is to get 1 bar of super by doing special moves and then enter DARK FORCE just before you beat your opponent.

Change your settings to the following :

Game Difficulty : 0
Attack Power : Maximum
Timer Speed : Slow
Lives : 1

Choose whichever character you are comfortable with. I chose Demitri.
When you start your fight either land some hits on your opponent or do special moves to build your meter/bar to 1 which you can see in the lower left corner. When I was using Demitri I kept doing Demon Cradle which is basically a Shoryuken from Street Fighter (

Once you have atleast 1 bar of meter keep damaging your opponent until they are close to being defeated.
When you only have to hit them once or twice more enter DARK FORCE(Push together)
Make sure you finish them while in DARK FORCE and if you do you will see it listed on the left side of the screen.

Now repeat this for 3 of the first 5 fights and you will then enter your extra battle and earn this achievement.

NOTE : You can use quicksaves every time before entering Dark Force to make sure you dont mess this up.