Far Realm Parasite. Inside the lich’s torso dwells a wormlike parasite that contains the lich’s soul. When the lich dies, it implodes into the parasite, which then vanishes into the Far Realm. In 2d4 days, the parasite causes the lich to reappear within 1d4 miles of where it died. If the lich died inside a magic circle cast to contain Undead, the lich instead reappears as an otyugh with all the lich’s memories.

Unusual Nature. The lich doesn’t need air, food, drink, or sleep.

Multiattack. The lich makes one Parasitic Tentacle attack or uses Spellcasting. The lich also uses Psychic Whisper twice.

Parasitic Tentacle. Melee Weapon Attack: +9 to hit, reach 10 ft., one creature. Hit: 25 (6d6 + 4) piercing damage plus 25 (6d6 + 4) necrotic damage. The target must succeed on a DC 17 Constitution saving throw or be poisoned. The poisoned target can repeat the save at the end of each of its turns, ending the effect on itself on a success. The third time the target fails the save, the target dies and dissolves into a gibbering mouther that obeys the lich and uses the target’s initiative.

Psychic Whisper. The lich targets one creature it can see within 120 feet of itself. The target must succeed on a DC 17 Wisdom saving throw or take 25 (6d6 + 4) psychic damage and be stunned until the end of the lich’s next turn as incomprehensible whispers fill the target’s mind.

Spellcasting. The lich casts one of the following spells, using Intelligence as the spellcasting ability (spell save DC 17):

At will: detect magic, mage hand, prestidigitation

2/day each: dispel magic, hunger of Hadar, lightning bolt

1/day each: arcane eye, dimension door, plane shift (self only)

when he has the chance he can summon both demons and skeletons as he lives in a grave yard  and all of them have Cthulhu's might they have enhanced strength and enhanced endurance and are at the command of the lich. he summons 4 of these soldiers to attack the party.

Far Realm Step. Immediately after taking damage, the lich, along with any equipment it is wearing or carrying, magically teleports up to 60 feet to an unoccupied space it can see.

Legendary Resistance (4/Day) 

Legendary Reaction: Eldritch Interference

When a creature targets one of the Eldritch Lich's summoned creatures with a spell or ranged attack, the Eldritch Lich can use this reaction to interfere with the attack. Roll a d20. On a roll of 15 or higher, the attack or spell targeting the summoned creature is redirected to a different valid target within range of the attacker's choice (if available). This ability can be used once per round.

Legendary Reaction: Soul Tether

When a summoned creature is reduced to 0 hit points, the Eldritch Lich can use this reaction to establish a soul tether. The summoned creature's life force is instantly transferred to the lich, healing it for an amount equal to the summoned creature's remaining hit points. Additionally, the Eldritch Lich gains temporary hit points equal to half the healed amount. This reaction can only be used once per round.

Legendary Reaction: Eldritch Retribution When a summoned creature is hit by a melee attack, the Eldritch Lich can use this reaction to unleash a burst of eldritch energy in retaliation. The attacker takes force damage equal to the damage dealt to the summoned creature. Additionally, the attacker must make a DC 17 Constitution saving throw, taking 6d8 psychic damage on a failed save or half as much on a successful one, as their mind is assaulted by otherworldly energies. This reaction can be used once per round.

Please note that you should adjust the damage and DC values to match the power level of your campaign and the Eldritch Lich's overall abilities. These legendary reactions add a layer of complexity and danger to the encounter, making the Eldritch Lich a formidable foe.

Legendary Action: Eldritch Strike Prerequisite: The summoned creature must be able to make a melee attack. The summoned creature makes a powerful melee attack against a target within its reach. This attack deals an additional 2d6 necrotic damage on a hit.

Legendary Action: Otherworldly Step Prerequisite: The summoned creature must have a movement speed. The summoned creature can use this legendary action to teleport up to 30 feet to an unoccupied space it can see. This allows it to quickly reposition itself on the battlefield to gain a tactical advantage.

Legendary Action: Dark Shielding Prerequisite: The summoned creature must have a reaction. The summoned creature can use this legendary action to protect itself or an ally within 30 feet. It grants the target resistance to all damage until the start of the summoned creature's next turn. This can be a lifesaver when your party is in a tough spot.

Eldritch Nova: The Eldritch Lich channels its darkest powers to unleash an Eldritch Nova, engulfing a large area in eldritch energy. This is a multi-step attack that unfolds over two rounds.

• Round 1: The Eldritch Lich begins charging the Eldritch Nova as its action. During this round, it cannot take any other actions. Dark energy crackles around the lich, and it becomes the focal point of the impending explosion.

• Round 2: On the lich's next turn, it releases the stored energy in a devastating explosion. All creatures within a 30-foot radius sphere centered on the lich must make a DC 20 Dexterity saving throw. On a failed save, a creature takes 15d10 force and 15d10 necrotic damage and is knocked prone. On a successful save, a creature takes half damage and isn't knocked prone. Structures and objects in the area take double damage.

The Eldritch Lich can only use Eldritch Nova once per long rest, as it drains a significant portion of its power.

1. Tendrils of Annihilation: The Eldritch Lich extends its bony hand, summoning shadowy tendrils from the void to ensnare its foes. This attack targets a single creature and has a chance to instantly destroy its target.

   • The Eldritch Lich makes a ranged spell attack against a creature it can see within 60 feet. On a hit, the target must make a DC 22 Constitution saving throw or suffer 10d12 necrotic damage. If this damage reduces the target's hit points to 0 or fewer, it is instantly destroyed, disintegrated by the eldritch power.

   This attack can be used once per day and is particularly terrifying because of its potential to erase a powerful enemy in an instant.