Blight Knight

Regeneration. The Knight Blight regains 15 hit points at the start of its turn. If the Knight Blight takes radiant or fire damage, this trait doesn't function at the start of the Knight Blight's next turn. The Knight Blight dies only if it starts its turn with 0 hit points and doesn't regenerate. 

Spellcasting. The Knight Blight is able to cast certain spells. Its spellcasting ability is Constitution (spell save DC 17, +9 to hit with spell attacks). The Knight Blight has following spells prepared:
Infestation (at will),
Stinking Cloud (1/day)
Contagion (1/day)

Stench. Any creature that starts its turn within 5 feet of the Knight Blight must succeed on a DC 17 Constitution saving throw or be poisoned until the start of its next turn. On a successful save, the creature is immune to the Knight Blight's Stench for 24 hours. 

Multiattack. The Knight Blight makes 2 attacks with its Bubotic Hammer

Bubotic Hammer. Melee Weapon Attack: +8 to hit, reach 5 ft., 1 target. Hit: 14 (2d8 + 4) bludgeoning damage and an additional 12 (3d6) necrotic damage. 

Head Toss (3/day). The Knight Blight tosses a rotting head to a creature within 30ft. The target must make a DC 17 Constitution saving throw. On a failed save, the target takes 8d6 necrotic damage and are poisoned for 1 minute. On a successful save, the target takes half as much damage and are not poisoned. The target can make the saving throw again at the end of each of its turns. 

Vermid Shield. As a reaction to being hit with a melee attack, the Knight Blight raises its shield. The Knight Blight's armor class increases by 2 until the start of its next turn. The attacker also takes 1d6 piercing and 1d6 poison damage.