Undead Nature.

Xel’nar doesn’t require air, food, drink, or sleep.

Forest Drain.

Whenever a creature within 30 feet of Xel’nar regains hit points from a natural source (healing spells, Goodberry, aura effects), it must make a DC 16 Constitution saving throw or take half the healing as necrotic damage instead.

Multiattack.

Xel’nar makes two Slam attacks and one Necrotic Spew.

Slam. Melee Weapon Attack: +11 to hit, reach 10 ft., one target.

Hit: 11 (2d10 + 6) bludgeoning damage plus 7 (2d6) necrotic damage.

Necrotic Spew (Recharge 5–6).

Xel’nar releases a cone of putrid energy in a 60-foot cone. Each creature in the area must make a DC 17 Constitution saving throw. On a failed save, the creature takes 45 (10d8) necrotic damage and is blinded until the end of its next turn. On a success, it takes half damage.

Raise the Husk.

Xel’nar reanimates a pile of corpses or dead creatures within 60 feet, creating 2d4 Husk Thralls (use zombie or ghoul stat blocks with spider/undead flavor). They act on initiative count 20 (losing ties), under Xel’nar’s control.

Corrupted Pulse (Recharge 4–6)

Xel’nar releases a surge of necrotic energy through the land. One creature within 60 feet that is restrained, prone, or grappled takes 10 (3d6) necrotic damage and has disadvantage on its next saving throw before the end of its turn.

Husk Command (No recharge)

Xel’nar issues a mental command to her Husk Thralls. Up to two undead under her control may immediately take a movement or melee attack action (no reaction cost to them).

Venomous Backlash (1/turn)

When a creature within 10 feet hits Xel’nar with a melee attack, she exudes a toxic burst. The attacker must succeed on a DC 16 Constitution saving throw or take 9 (2d8) poison damage and be poisoned until the end of its next turn.

Instinctive Reposition (1/turn)

When targeted by a ranged spell or attack she can see, Xel’nar moves up to 20 feet without provoking opportunity attacks. She must end this movement behind partial cover (if any is available).

Tremble the Roots (1 action).

All terrain within 30 feet of Xel’nar quakes. Each creature in that area must succeed on a DC 16 Dexterity saving throw or fall prone.

Sap Drain (2 actions).

Xel’nar targets one creature it can see within 60 feet. That creature must make a DC 18 Constitution saving throw or take 18 (4d8) necrotic damage and have its healing halved until the end of its next turn.

Burst Husk (3 actions).

Xel’nar causes a Husk Thrall within 30 feet to violently explode. Each creature within 10 feet of the thrall must make a DC 16 Dexterity saving throw or take 21 (6d6) necrotic damage and be blinded for 1 round.