Baknork

Heated Body. Every creature that starts its turn within 5 ft of the Baknork takes 2d6 fire damage and take the same damage on a successful melee weapon hit.

Of the Mortem. While the Baknork is in the Mortem, it gets advantage on saving throws.

Devil's Sight. Magical darkness doesn't impede the imp's darkvision.

Multiattack. The Baknork makes two attacks: all with its punch.

Punch. Melee Weapon Attack: +10 to hit, reach 20 ft., one target. Hit: 17 (2d12 + 5) bludgeoning damage. 

Breath Weapon. Ranged Weapon Attack: range 20/120 ft., every creature in a 120 foot-cone in front of the Baknork makes a DC 15 Dexterity saving throw. They take 3d12 fire damage on a failed save and half as much on a successful one.