Prerrequisites:
-Soul gem. You need to capture at least a soul from a particular enemy to get this achievement.

Recommended:
-Halo, to make it faster. Also this should be your very first item.
-1 or 2 health upgrades. I used just one but you depend on luck to get it this way. With full health upgrades you don't depend on luck.

Demonstration:

How-to
1. From the start go six rooms to the right and one down. Kill the four bats at that room to gain access to the secret area.


2. In this secret area there is a fairy jailed. Hit the jail with Pampas' sword to liberate her. Touching her will heal you and give you the Soul Mastery special.
NOTES:
-Freeing the fairy and leaving the room without touching her will give you the Prisoner of War achievement.
-This is not really mandatory but it is pretty much easier to get the special we need by using Soul Mastery.

3. Use the Halo to return to the starting area. From there go up two rooms. You will find two snakes and three barrels. Activate the Soul Mastery special but DON'T touch the barrels yet.


4. Kill a snake to get the Conjure Apples special. You can use it three times to conjure tree apples each use.


5. Use the fire trap and the venom from the other snake to get low health with both characters. If you have a lot of health upgrades you don't need to hurt them so much.


6. Destroy the three barrels. If you lucky you will find at least an apple. You only need one.
If you have a lot of health upgrades you can look for an apple at another room if you don't find one here.
If you don't have health upgrades and don't find an apple here go to a room with enemies and barrels. Destroy the barrels to get an apple and use the enemies to hurt you if you need it. You can also use Selene's Fireball to hurt you if you have it.


7. Use the Conjure Apples special to do exactly that, conjure apples. Eat nine from the special and one from the barrels. If you get full health with both characters use the fire trap again to lose some health and keep eating apples. Do not leave the room without eating ten apples.