Cain, Demon of Death

Death Beyond Death (Recharges after a Short or Long Rest). If Cain would be reduced to 0 hit points, his current hit point total instead resets to 250 hit points, he recharges his Breath Weapon, and he regains any expended uses of Legendary Resistance. Additionally, the Cain can now use the options in the “Mythic Actions” section for 1 hour. Award a party twice the XP for defeating Cain after his Death beyond death feature activates.

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

Devil’s Sight. Magical darkness doesn’t impede the Cain’s darkvision.

Free Animator. When Cain casts the spell Animate Dead  or a similar spell he does not require a corpse or skeleton to cast it, instead they burst out of the ground. In addition, Cain casts said spells with a casting time of 1 action.

Innate spellcasting. Cain's spellcasting ability is Charisma (spell save DC18). He can innately cast the following spells, requiring no material components.

At-Will: Animate dead (4th-level)

3/day each: Blight, Danse Macabre, Vampiric Touch

1/day each: Finger of Death, Negative Energy Flood

Magic Weapons. Cain's weapon attacks are magical.

Marshal Undead. Unless Cain is incapacitated, he and undead creatures of his choice within 60 feet of him have advantage on saving throws against features that turn undead.

Polearm Master. If a creature enters Cain's reach they provoke an opportunity attack from him.

Reactive. Cain can take a reaction on every turn of combat.

Sentinel. When a creature provokes an opportunity attack from Cain, if he hits the target's speed becomes 0. In Addition, Cain can still make an opportunity attack even if they use the disengage action beforehand.

Sunlight Hypersensitivity. Cain, like all other demons, takes 20 radiant damage when he starts his turn with at least half his body in sunlight. The effects of the sun are negligible with less than half his body in the sunlight.

Undead Nature. Cain doesn't require Air, Drink or Sleep. However, he still must feed to satiate his hunger.

Undying Nature. Cain's demonic nature makes him immune to death in most instances. Whenever Cain would be dropped to 0 hitpoints, he makes a constitution saving throw with a DC equal to the amount of damage taken. On a successful save he instead drops to 1 hit point. This feature doesn't activate if he was dropped to 0 hit points as a result of taking radiant damage or damage from a critical hit.

Multiattack. Cain can make three scythe attacks, one of these attacks can be replaced by Wails of Death or Sow the Weak, if available.

Grip of Death. Melee Weapon Attack: +9 to hit. Reach 5ft., one target. Hit:  16 (3d8+3) necrotic damage, if the target is a creature they must make a DC20 constitution saving throw or gain one stack of marked.

Scythe. Melee Weapon Attack: +11 to hit.  Reach 10ft., one target. Hit: 10 (1d10+5) slashing damage plus an additional 4 (1d8) necrotic damage. 

Sow the Weak. Cain targets a creature with at least one stack of marked, that creature must make a DC20 constitution saving throw and removes all stacks of marks. On a failed save that creature takes xd10 necrotic damage where x equals the number of stacks consumed, taking half damage on a successful save. In either case, Cain heals for an amount equal to the necrotic damage dealt.

Wails of Death (Recharge 6). Each creature within 120ft who has killed a humanoid must make a DC20 wisdom saving throw. On a failed saving throw each creature takes 26 (4d12) necrotic damage and 26 (4d12) force damage and frightens the creature until the end of their next turn. While frightened in this way the creature is also considered paralyzed.

Despair of the Damned (Once per Short Rest). Each creature within 120ft. of Cain who is marked, or suffers from a curse or disease must make a DC20 Wisdom Saving throw or take 5 (1d10) necrotic damage and become paralyzed. On a failed save the target instead takes 11 (2d10) poison damage.

Free the souls (once per short rest). Cain summons 11 (2d10) skeletons and 2 (1d4) zombies.

The Mark of Damnation. Cain chooses 3 creatures within 60ft of him, that must make a DC20 constitution saving throw, on a failed save the creature gains a stack of marked. For each stack of mark attached to a creature, they take an additional d6 of necrotic damage when hit with a melee attack by Cain.

Apply Poison (3/Short Rest). Cain can apply Wyvern poison to his Scythe. When he hits with the blade while this poison is applied the creature must make a DC15 constitution saving throw or take 24 (7d6) poison damage. Taking half as much damage on a success. If Cain attacks and misses while the poison is applied it stays applied until he hits a target.

Link Souls. Cain spends a point of marked from two separate creatures who are within 60ft of each other while one is within 60 feet of Cain. While linked, when one creature takes damage halve it after resistances, the other creature takes the same amount in force damage.

Pommel Strike. Melee Weapon Attack: +11 to hit. Reach 10ft., one target. Hit:  7 (1d4+5) bludgeoning damage. In addition the creature should make a DC17 strength saving throw or be knocked prone.

Hinder the living. Cain targets a creature who succeeds on a saving throw he caused or hits him with an attack roll, Cain may expend any number of marked and remove that amount from the total, possibly causing the attack to miss.

Sentinel's Strike. If a creature hits a target other than Cain while within Cain's reach, he may make a melee weapon attack against them.

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.

Scythe. Cain makes a single Scythe attack.

Cast (2 actions). Cain casts a spell from his Innate spellcasting feature.

Ignorance (3 actions). Cain surges with energy, each creature within 60ft. of him must make a DC20 constitution saving throw or become marked as in his The Mark of Damnation Bonus action.

If Cain's Death Beyond Death trait has activated in the last hour, it can use the options below as legendary actions.

Teleport. Cain can teleport to a point he can see within 120ft.

Shadowed Veil (3 actions). Cain can grant himself immunity to Bludgeoning, Piercing and Slashing damage until the start of his next turn.