Cipactli

Amphibious. The cipactli can breathe air and water.

Multiattack. The cipactli uses its consuming presence and then makes three attacks: two with its lesser bite and one with its greater bite.

Lesser Bite. Melee Weapon Attack: +8 to hit, reach 5 ft., 1 target. Hit: 10 (1d10 + 5) piercing damage. 

Greater Bite.  Melee Weapon Attack: +8 to hit, reach 5 ft., 1 target. Hit: 27 (4d10 + 5) piercing damage, and the target is grappled (escape DC 16). Until the grapple ends, the target is restrained and the cipactli cannot use its greater bite on another target.

Consuming Presence. Each creature of the cipactli's choice that is within 60 feet of it must succeed on a DC 15 Wisdom saving throw or suffer a level of exhaustion for 1 hour. If an affected creature already suffers a level of exhaustion, that exhaustion increments by one level to a maximum of level 6.

Vengeful Bite. If the cipactli takes damage from a melee attack while the attacker is within 5 feet of the cipactli, the cipactli may use its reaction to make two lesser bite attacks against the attacking creature.

Opportune Bite. If a creature within 5 feet of the cipactli makes an attack against a target other than the cipactli, the cipactli may use its reaction to make a lesser bite attack against the attacking creature.