Duergar Resilience. The duergar has advantage on saving throws against poison, spells, and illusions, as well as to resist being charmed or paralyzed.

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

Death Domain. Channel Divinity 1 use per rest

Reaper. A necromancy cantrip can target two adjacent enemies

Touch of Death. on a melee attack that hits the cleric can use channel divinity to deal an additional necrotic damage of 5+ twice the cleric level 

Enlarge (Recharges after a Short or Long Rest). For 1 minute, the duergar magically increases in size, along with anything it is wearing or carrying. While enlarged, the duergar is Large, doubles its damage dice on Strength-based weapon attacks (included in the attacks), and makes Strength checks and Strength saving throws with advantage. If the duergar lacks the room to become Large, it attains the maximum size possible in the space available.

WarHammer. Melee Weapon Attack: +4 to hit, reach 5 ft., one target. Hit: 6 (1d8 + 2) bludgeoning damage, or 11 (2d8 + 2) bludgeoning damage while enlarged.

Javelin. Melee or Ranged Weapon Attack: +4 to hit, reach 5 ft. or range 30/120 ft., one target. Hit: 5 (1d6 + 2) piercing damage, or 9 (2d6 + 2) piercing damage while enlarged.

Invisibility (Recharges after a Short or Long Rest). The duergar magically turns invisible until it attacks, casts a spell, or uses its Enlarge, or until its concentration is broken, up to 1 hour (as if concentrating on a spell). Any equipment the duergar wears or carries is invisible with it.

Spellcaster The Duergar is a 4th level spellcaster. spellcasting ability is Wisdom (spell save DC 14 +6 to hit with spell attacks) The Duergar has the following cleric spells prepared

Cantrips (at will) Toll the dead, Spare the dying, resistance, Sacred Flame, Guidance

1st level (4 slots) False Life, Ray of Sickness, Bane, Inflict Wounds, Cure Wounds, Shield of faith

2nd level (3 slots) Blindness/Deafness, Ray of Enfeeblement, Hold person, Lesser restoration