Corrupted Azazel

Outerplane Protection No power of the dead can harm this creature, as the forces from beyond the physical plane that bind them to this earth now shields them from harm. Azazel gains resistance to Necrotic Damage, and immunity to cold damage

Mind Meld. Given Azazels brain is subjected to the forces beyond his understand, his mind once full or rational thought is now devolved into a pile of slop as he has became controlled by Tantibus. Azazel is immune to psychic damage, but has disadvantage on Charisma saving throws.

Spellcasting. Azazel is a 10th level spellcaster. Its spellcasting ability is +9. Azazel, in their newfound power has following Warlock spells prepared:
Cantrips (at will): Eldritch Blast, Toll of the Dead, Chill Touch, Prestidigitation
5th level (5 slots): Armor of Agathys, Witch Bolt, Danse Macabre, Thunder Step, Call lightning, Haste

Connections. Due to his heart belonging to Tantibus, he may call for assistance from Nightmare Moon for more aid. Can summon up to five Night Guards and one Night Walker. After use, the subject must complete a long rest in order to use again

A Call Beyond. Clasping his hands together Azazel calls upon the powers of Tantibus to take down his foes, as astral Beams of light summon from a void in order to take down up to 3 foes of his choosing. Targets must succeed on a Dex saving throw of be pierced with these beams of light. Azazel has two uses of this before he is unable to call anymore.

Moon Sickle +3 Melee Weapon Attack: +7 to hit, reach 5 ft., 1 target. Hit: (2d4 + 7) Slashing damage. 

Astral Bow. Ranged Weapon Attack: +7 to hit, range 20/400 ft., 2 target. Hit: (2d10 + 4) piercing damage. Upon release of the arrow Azazel chooses 1 of the 3 possible damage types for the attack.

1) Freezing Arrow. The whiz of cold pierces into the enemy and physically encapsulates a part of the targets body. Target takes 2d6 freezing damage and halves their movement speed for 2 rounds

2) Chilling Arrow. A chilling feeling grows in the targets mind upon successful shot. Target takes 2d10 necrotic damage and must make a constitution saving throw or become frightened for 2 rounds

3) Fire Arrow. Target takes 4d8 Fire damage and becomes burned for 1 additional round. Burn damage is 1d8 extra before the flame dies out.

Two-Weapon Fighting. Azazel gained the ability to duel wield a sword, as well as summon an astral blade to be able to fight his opponents. He may only use this ability for one action every 4 turns of combat he has gone through, as this ability takes a toll on his fleshy form every time he uses it.

Astral Rebuke. Upon being attacked, the creature who is making the attack against Azazel must succeed upon a Dex saving throw, or be enveloped in turquoise blue flames. It takes 2d10 fire & necrotic damage upon a failed save, half as much if said creature makes a successful one.

Spectral Parry. Upon being attacked with a slashing or piercing weapon, Azazel can make a Dex saving throw in order to attempt to parry the oncoming attack with a spectral sword to take no damage. Target must also make a Dex saving throw to compete. Upon failure, Azazel recieves the full damage of the attack.