Vengeance Demon

Type: Demon
Language: common and infernal
The Creature can't make attacks or bonus actions while it is out of the hosts body but the creature can only often take over cursed hosts. The hosts alignment automatically turns to chaotic evil and they are immune to being frightened for the duration while it is possessed. Your movement also increases by 10. The creature also radiates dark black smoke from it's body and eyes. When that happens the vengeance creature acts as if it's the host with all its same thoughts and ideals but must take actions bloodlusted. The creature must then make a roll on a d100, if it lands between a 100 and 60 you are completely controlled by the DM for the duration, If it lands on 40 or below you are still possessed but have the strength to fight off the demons that tried to control your mind. If a possessed creature fails the roll the DM can attack any creature within the hosts ranged weapon distance. This effect lasts until a marked creature drops to 0 HP or 10m has passed. Only then does the demon rest dormant until your next long rest.

For the duration the hosts ranged weapons causes a extra 3d8 necrotic damage to its attacks. 

While possessed the creature can make a bonus action and activate "Vengeful Shots" to carve its victims names magically into the host ranged weapons. The names written on the weapons radiates bright light 5ft from the creature and dim light 10ft from it. The creature also tires to shove fear into its enemies, every foe considered a enemy that has attacked the possessed host must make a  DC constitution save or be frightened by the creature. Each frightened creature has disadvantage to its next attack. A passed DC has no effect.

When a possessed creature drops another creature to 0 Hp the creature boosters with health as its demon eats the dying soul. The possessed creature regain 5 + your dexterity modifier + your constitution modifier hit points.