Incorporeal Movement. Thaklmir can move through other creatures and objects as if they were difficult terrain. It takes 5 (1d10) force damage if it ends its turn inside an object.

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

Shadow Sight. Magical darkness doesn’t impede Thaklmir's darkvision.

Shadow Stealth. While in dim light or darkness, Thaklmir can take the hide action as a bonus action.

Sunlight Sensitivity. While in sunlight, Thaklmir has disadvantage on attack rolls, as well as on Wisdom (Perception) checks that rely on sight.

Spellcasting. Thaklmir is a 9th-level spellcaster. His spellcasting ability is 20. Thaklmir has following  spells prepared:
Cantrips (at will): Light, True Strike, Shocking Grasp, Booming Blade
1st level: Bane, Bless, Divine Favor, Thunderwave, Sleep, Entangle, Shield, Mage Armor

2nd level: Arcane Lock, Blindness/ Deafness, Gentle Repose, Levitate, Invisibility,

3rd level: Dispel Magic, Fly, Gaseous form, Major Image, Hypnotic Pattern,

4th level: Banishment, Dimension Door, Conjure Minor Elementals, Dominate Beast, Phantasmal killer, Guardian of Faith,

5th Level: Arcane Hand, Awaken, Conjure Elemental, Contagion, Contact Other Plane,

6th level: Flesh to stone, Move Earth, Programmed Illusion, Disintegrate, Conjure Fey

7th level: Conjure Celestial, Plane Shift, Divine Word, Reverse Gravity

8th level: Earthquake, Dominate Monster, Feeblemind, Holy Aura, Power Word Stun

9th Level: Astral Projection, Gate, Foresight, Imprisonment, Meteor Swarm, Power Word Kill, Storm of Vengeance, Shapechange, Wish

Homebrew: Deify (Unable to use while undead, learned after death), Summon Worldbreaker (Summons Undead Prismatic Dragon)

Life Drain. Melee Weapon Attack: +7 to hit, reach 5 ft., one creature. Hit: 28 necrotic damage and the target’s hit point maximum is reduced by an amount equal to the damage taken. This reduction lasts until the target finishes a long rest. The target dies if this effect reduces its hit point maximum to 0.

Shadow Walk (3/day). As a bonus action while in dim light or darkness, Thaklmir can teleport to an unoccupied space it can see within 30 feet that is also in dim light or darkness.