His Title is "Vengance"
His character description says "Make them pay"
Light Jacob's Title is "ReConnection"

Maybe you could have a swap item that lets you switch souls with light Jacob and they have different ability's

Unlock method:
on alt jacob die in sacriface room on first floor. Then you will be teleported in sheol as dark esau. You ascending up to home then when you in home bomb TV and go to the angelic door. When you in fight 4 angels and then boom - you have Tarnished jacob.
gameplay:
You playing as Esau with light jacob. After 20 seconds light jacob will apper and if he touches Esau, He will stun you for 5 seconds. he can summon light beams and throw anima soul. Pocket item is "devil wrath" that summons devil that kills light Jacob for 15 seconds and have 6 rooms charge. After 30 seconds he will appear again and if he touches Esau he will stun him for 8 seconds (upon each use the stun time is increassing by 3).
Stats:
1.2 speed
2 tears rate
4.5 damage
6 range
1 shot speed
-1 luck