Actions

Multiattack
The demon makes three attacks, one of which can be with its Blackreek Maw OR it's Tormenting Maw
Blackreek Maw-
Melee Weapon Attack: +9 to hit, reach 5 ft., one target. Hit: 16 (2d10 + 5) piercing plus 14 (4d6) poison damage.   Dragging Graspers-
Melee Weapon Attack: +9 to hit, reach 10 ft., one target. Hit: 14 (2d8 + 5) slashing damage and the target is grappled (escape DC 17).
Tormenting Maw-
Melee Weapon Attack: +9 to hit, reach 5 ft., one target. Hit: 45 (6d12 + 6) piercing damage and the target is grappled (escape DC 19).
Poison Skin-
The skin of a creature grappled by the demon begins to recede from its touch, revealing muscle and sinew beneath.
The target begins Bleeding (1d8, Save Ends at end of turn) and must succeed on a
DC 16 Constitution saving throw or take 2d10 necrotic damage, or half as much on a success.

Reactions

Yawning Howl-
When the demon is reduced below 117 hit points, it can tear each of its mouths wide and howl forth a torrent of pestilence in a 30 foot cone. Each creature in the area must succeed on a DC 17 Constitution saving throw or be infected with Blackwort's disease.
Beasts fail this saving throw automatically.
Blackwort's disease-
A creature infected with Blackwort's Disease has painful nodules swell rapidly beneath its flesh.
After each 1d4 hours the creature remains infected, one of the nodules bursts; the infected creature has its current and maximum hit points reduced by 5 (1d10) until this disease is cured, and each creature within 5 feet of it must succeed on a DC 17 Constitution saving throw or contract Blackwort's disease. When an infected creature completes a long rest, it must succeed on a DC 17 constitution saving throw.