Soul Complementation

Your soul has special properties that allow you to connect with free souls and let them into your body. This gives you a pool of soul charges equal to your charisma value. You can use souls from this pool to gain one of the following properties:

• When you cast a spell, you can strengthen it. Spending charges in an amount equal to the spell's level, you add +4 DC against it.
  Spend charges equal to the spell's level, you add +4 DC against it.
• With the bonus action, you can get temporary HP equal to the spent charges. They end with a short rest.
• If your pool has less than half its charges and a creature dies within 30 feet of you, you can spend a reaction to consume that soul. To do this, you need to make a save throw of charisma with a difficulty equal to 10 + 1/2 CR of the creature. You can use this number of times equal to the proficiency bonus.

The pool is recovering on long rest. To restore it completely, you need to make a save throw of 13 DC charisma.
(The pool increases by 5 points at 11 and 17 levels)