Spellcasting. Zeltra is an 18th-level spellcaster. his spellcasting ability is Intelligence +9 to hit with spell attacks). 

Cantrips (at will) Chill Touch, Spare the Dying 

1st level (2 slots): Inflict Wounds, False Life

2nd level (3 slots): Blindness/Deafness, Ray of Enfeeblement, Gentle Repose

3rd level (5 slots): Animate Dead, Bestow Curse, Revivify, Speak with Dead, Vampiric Touch

4th level (1 slots): Blight

5th level (1 slots): Contagion

6th level (6 slot): Globe of Invulnerability, Circle of Death, Create Undead, Eyebite, Harm, Magic Jar

7th level (3 slot): Teleport, Finger of Death, Resurrection

8th level (1 slot): Clone

9th level (1 slot): Astral Projection, True Resurrection

Multiattack. Zeltra attacks twice. can only attack with spellcasting or poison spray once per turn.

(x2)Scimitar. Melee Weapon Attack: +2 to hit, reach 5 ft., one target. (1d6) slashing damage.

Poison spray. Ranged Weapon Attack: +5 to hit, range 10 - 10 ft square. (4d4) poison damage.