Zarzul is a 20th level spellcaster. His spellcasting ability is intelligence (spell save DC: 22, +14 to hit with spell attacks). Zarzul has the following Wizard spells prepared:
Rejuvenation. If it has a phylactery, a destroyed lich gains a new body in 1d10 days, regaining all its hit points and becoming active again. The new body appears within 5 feet of the phylactery. Turn Resistance. The lich has advantage on saving throws against any effect that turns undead.
Paralyzing Touch. Melee Spell Attack: +12 to hit, reach 5 ft., one creature. Hit: 3d6 cold damage. The target must succeed on a DC 18 Constitution saving throw or be paralyzed for 1 minute. The target can repeat the saving throw at the end of each of its turns, ending the effect on itself on a success
Zarzul 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. Zarzul regains spent legendary actions at the start of his turn. Cantrips. Zarzul can cast a Cantrip. Paralyzing Touch (Costs 2 Actions). Zarzul can use his Paralyzing Touch attack. Frightening Gaze (Costs 2 Actions). Zarzul fixes his gaze on one creature he can see within 10 feet of him. The target must succeed on a DC 18 Wisdom saving throw against this magic or become frightened for 1 minute. The frightened target can repeat the saving throw at the end of each of its turns, ending the effect on itself on a success. If a target's saving throw is successful or the effect ends for it, the target is immune to Zarzul's gaze for the next 24 hours. Disrupt Life (Costs 3 Actions). Each non-undead creature within 20 feet of Zarzul must make a DC 18 Constitution saving throw against this magic, taking 21 6d6 necrotic damage on a failed save, or half as much damage on a successful one.
On initiative count 20 (losing initiative ties), Zarzul can take a lair action to cause one of the following magical effects; Zarzul can't use the same effect two rounds in a row:
Zarzul's Lair is a network of cave systems carved into a mine entrance which he scrapped and turned into a maze. It's a large winding cacophony of tunnels, traps, dead ends, endless hallways, boss rooms, and if someone manages to surpass the 7000 different possible outcomes of the lair over 80% of them resulting in immediate or instantaneous death, then a seemingly endless winding stairwell leading up to Zarzul's study where he resides. In here he possesses knowledge of every spell ever created and has knowledge of spells that have not even come into existence yet.
Zarzul used to be a herbalist who tended to the ill within a village. He quickly became corrupt with power and desire for immortality and godhood. He researched the process and the aftermath of Lichdom. He prepared the ritual and quickly took care of the necessary precautions to ensure its success. He succeeded in reaching Lichdom and quickly moved to the mountains beyond the village in fear of his phylactery being destroyed. He contacted Asmodeus the Lord of Nine Hells, to grant him a contract so he could have more protection and safety in his lair. Using the necromantic power's Asmodeus granted him he created an army of skeletons, zombies, and his favorite of his creations his Gashadokuro. A 120ft tall monstrosity resembling a skeleton with enormous shackles on its hands and feet.
A vividly crafted, networked, and carved cavern that has over 700 different entrances, exits, dead ends, and hallways, some of which lead on infinitely. In the center of the maze and finally the peak of the mountain is Zarzul who resides in his study.