Deal with the Devil is a new game mechanic added in version 20220811.
When you leave the safe house for the first time after the Prologue, Mephisto will now talk to you.
He purposes you to sell a percentage of your soul to him in exchange for certain benefits that he can provide.
You will learn a new skill: Deal with the Devil. (Instant act, you can use this skill for an unlimited amount of time during each turn in a battle.)
You can use this skill at any time, during a battle, or from the menu.
You can ask him for more details and check what he offers.
However, if you lose 100% of your soul, it will be game over. (More details can be found in Mephisto's conversation with you.)
Relationship with Mephisto can be improved when you sign a deal with him. However, it's not recommended.
You can give other human's soul to get your soul back from Mephisto.
However, other human souls only worth 1% of your soul.
You can harvest other human's soul via using a soul sickle.
| Effect | Cost | Requirement |
|---|---|---|
| Restore your HP | 1% of your soul | |
| Restore your MP | 1% of your soul | |
| Spell Book: Darkness | 2% of your soul | Not in a battle. |
| Skill Book: Devour Corpse | 2% of your soul | Not in a battle. |
| Stun Nearby Hostiles | 5% of your soul | Not in a battle. |
| Pet: Fire Imp | 5% of your soul | Not in a battle. Group is not full. |
| Summon a Gunsmith from the Hell | 2% of your soul | Not in a battle. |
| Demonic Knowledge (+66% Mgi. until the end of the battle) | 2% of your soul | In a battle. Don't already have this bonus. |
Fun facts:
A deal with the Devil is also called a Faustian bargain or Mephistophelian bargain: https://en.wikipedia.org/wiki/Deal_with_the_Devil
And, it is Mephisto that makes deals with you in the game.