Cain Blackthorne

 Legendary Resistance (3/Day). If Cain fails a saving throw, it can choose to succeed instead.

Magic Resistance. Cain has advantage on saving throws against spells and other magical effects.

Brute. A melee weapon deals one extra die of its damage when Cain with it (included in the attack).

Burning Rage. Each time Cain loses 50 hit points, add a tally mark. Each tally gives him one Fireball. Upon reaching 3 tally's, or losing 150 hit points, he can unleash Hellish Expulsion. Hellish Expulsion uses all 3 tally's, while each Fireball uses 1. It maxes at 3.

Innate Spellcasting. The pit fiend's spellcasting ability is Charisma (spell save DC 21). The pit fiend can innately cast the following spells, requiring no material components:

At will w/ tally: fireball

With 3 tally's: Hellish Expulsion (note; search homebrew for this spell. Found out we cant add homebrew spells to homebrew monsters)

Hellish Rebirth. Upon Cain Blackthorne being killed, his flames go out, and he lies lifeless. Within 1d10 days, Cains embers will reignite, and he will come back to life, regaining all his hit points and becoming active again.

Multiattack. Cain makes three melee attacks or two ranged attacks.

Unarmed Strike. Melee Attack Roll: +5, reach 5 ft. Hit: 5 (3d6+10) Bludgeoning damage.

Hellborne Blade. Melee Weapon Attack: +15 to hit, reach 5 ft., one target. Hit: 47 (7d10 + 10) slashing damage plus 27 (6d8) burning damage.

Arm Mounted Crossbow. Ranged Weapon Attack: +3 to hit, range 80 ft./320 ft., one target. Hit: 17 (3d8 + 9) piercing damage.

Parry. Cain adds 3 to its AC against one melee attack that would hit it. To do so, Cain must see the attacker and be wielding a melee weapon.

Killer Instinct. Upon attacking Cain, he can Lock in and roll to counter the attack with an unarmed strike, or an attack with his blade.

Cain can take 3 legendary actions, choosing from the options below. Only one legendary action option can be used at a time and only at the end of another creature’s turn. Cain regains spent legendary actions at the start of its turn.

Move. Cain moves up to its speed without provoking opportunity attacks.

Unarmed Strike. Cain makes one unarmed strike.

 Hellborne Blade. Cain makes one attack with his Hellborne Blade

Expert tactician (Cost 3 Action). Using his years of knowledge, he can attempt to predict the players movements, rolling a wisdom check. Upon succeeding, all attacks on him are at disadvantage until his next turn. Upon failure, nothing happens.