Spellcasting. The Nemetoa is a 5-level spellcaster. Its spellcasting ability is Charisma (spell save DC 15, +7 to hit with spell attacks). The Nemetoa has following Cleric spells prepared:
Cantrips (at will): Animal Friendship (snakes only), Guidance, Mending, Resistance, Sacred Flame
1st level (4 slots): Bane, Command, Guiding Bolt, Inflict Wounds
2nd level (3 slots): blindness/deafness, Hold Person, Spiritual Weapon
3rd level (2 slots): Beacon of Hope, Dispel Magic

Magic Resistance. The nemetoa has advantage on saving throws against spells and other magical effects.

Multiattack. The nemetoa makes three melee attacks, but can only use its Bite and Constrict attacks once each.

Bite. Melee Weapon Attack: +7 to hit, reach 5 ft., one target. Hit: 7 (1d6+4) piercing damage and 10 (3d6) poison damage. 

Constrict. Melee Weapon Attack: +7 to hit, reach 10 ft., one target. Hit: 11 (2d6+4) bludgeoning damage, and the target is grappled (escape DC 14). Until this grapple ends, the target is restrained, and the nemetoa can't constrict another target. 

Obsidian Knife. Melee Weapon Attack: +7 to hit, reach 5 ft., one target. Hit: 11 (2d6+4) slashing damage.