Multiattack

The yavalnoi makes three attacks: one with its bite, one with its claw, and one with its tail.

Bite

Melee Weapon Attack: +6 to hit, reach 5 ft., one target. Hit: 14 (2d10 + 3) piercing damage.

Claw

Melee Weapon Attack: +6 to hit, reach 5 ft., one target. Hit: 7 (1d8 + 3) slashing damage.

Tail

Melee Weapon Attack: +6 to hit, reach 10 ft., one target. Hit: 10 (2d6 + 3) bludgeoning damage.

Luminous Burst (Recharge 5-6)

The anchor-shaped organ atop the yavalnoi's head emits a burst of blue light. Each hostile creature within 30 feet of the yavalnoi must succeed on a DC 15 Wisdom saving throw or be outlined in blue light for 1 minute. While outlined in blue light, a creature can't breathe underwater. This effect dispels spells such as water breathing and temporarily suppresses water breathing granted through magic items or a creature's natural physiology. In addition, the yavalnoi and creatures friendly to the yavalnoi have advantage on attack rolls against creatures outlined in blue light. A creature outlined in blue light can repeat the saving throw at the end of each of its turns, ending the effect on itself on a success.

Call of the Deep (1/Day)

The yavalnoi magically calls 2d4 giant crabs or 1 giant octopus. The called creatures arrive in 1d4 rounds, acting as allies of the yavalnoi and obeying its spoken commands. The beasts remain for 1 hour, until the yavalnoi dies, or until the yavalnoi dismisses them as a bonus action.