Viperfiend

Creeping Darkness. While in dim light or darkness, the Viperfiend is under the effects of invisibility for creatures without darkvision, and heavily obscured for creatures with darkvision. 

Innate Spellcasting. Its spellcasting ability is Intelligence (spell save DC 18, +7 to hit with spell attacks). The Viperfiend has following  spells prepared:
Cantrips (at will): Chromatic Orb, Darkness, Incite Greed, Friends. 

Venomous Bite. Melee Weapon Attack. +7 to hit, reach 5ft., one target. Hit: 10 (2d6+3) piercing damage plus 7 (2d6) poison damage. 

Barbed Constriction. Melee Weapon Attack: +7 to hit, reach 10 ft., one target. Hit: 8 (1d8+3) piercing damage, and the target is grappled (escape DC 13). Until this grapple ends, the creature is restrained and takes 4 (1d6) piercing damage every round, and the Viperfiend cannot constrict another target. . 

Hypnotic Song. The Viperfiend targets all creatures within 60 ft. of it. If the target can hear the Viperfiend, the target must succeed pm a DC 18 Intelligence saving throw or be charmed for 1 minute. On every turn while this effect is active, the target can only move 20 ft. closer to the Viperfiend. The target can repeat the saving throw at the end of each of it's' turns, ending the effect on itself on a success. 

If the target's saving throw is successful, or the effect ends on it, the target is immune to the song for one hour. 

Move. The creature may take half of its movement as a bonus action. 

Venomous Bite. Melee Weapon Attack. +7 to hit, reach 5ft., one target. Hit: 10 (2d6+3) piercing damage plus 7 (2d6) poison damage.