Lost Souls: 2
Once in control, turn around before moving to find a copper key behind you.
Keep running and quickly destroy/ avoid enemies before the time runs out. After pulling a platform and crossing a long chasm, turn around and you should see the first of the two souls in this area.
Lost Soul 1, Secret Ingredient
After freeing the soul, continue to the end of the tunnel and pull the hatch open. Continue to the end of the tunnel to reach the next area. Once in control and before moving forth, turn to the left to find another lost soul.
Continue past the divinity statue but don't enter the door yet. Turn to the left to find a copper door. Use the key you acquired earlier to access the secret mission. (Copper – Rapid Descent) After completing the secret mission, enter the next door for a boss battle.
The boss has three life bars. It only has a swipe attack and a shockwave that will blow you away. You can easily avoid getting damaged by properly timing your evade before the swipe connects. There are three platforms in the area. Start off by moving to any of the left or right platforms then engage the boss there. After depleting the life bar, one of the two hanging tubes will be highlighted. Pull it then quickly return to the central platform before the current platform you're in gets destroyed. Repeat the process on the other platform then finally, engage the boss in the last platform. After the boss gets drowned in the pool, quickly leave the platform and return to the previous area.
One old, ugly sack of ****
After leaving, you'll be back in the previous area. The boss will appear again and you just have to use demon pull and angel lift as prompted. Once you're in the last platform, attack the Succubus' hand to weaken its grasp and to get shredded by the large fan.
After the scene, you'll obtain a new weapon called Eryx.