Demonic Brand

Your very soul is branded, you are now bounded to the demonic mark left on you. You also gain the ability of literal demon and will use those abilities to the fullest. These are the abilities given with the feat...

Ghastly Hunger - Once you hit 0 HP, instead of falling unconscious your soul will unbind from the body and if you deal damage that lasts about 1 combat turn (6 seconds), you will be given the same amount of HP from the damage you dealt. (This won't work to construct or undead) If you manage to not deal any damage, the soul will return to your body and now you will throw death saves.
Presence of Terror - You get advantage in Charisma (Intimidation) ability check. This ability only works to non-demonic creatures. Discuss with your DM what creatures will be affected by this ability
Demonic Links - Every time you rest outside of an accommodation Ie: other than an inn, tavern, or a town. The feat user will have to roll an opposing d20 roll to see whether the party will be ambushed by demonic creatures (This ranges from skeletons, zombies, or lesser demons). The feat user also will rest for half the time an actual rest would take (Short rest takes half an hour or an hour and long rest takes 4 hours). This can also cause exhaustion to the user. Again, arrange this with the DM with how it is managed