Awakened Giant Nautilus

Charge. If the Awakened Giant Nautilus moves at least 20 feet straight toward a target and then hits it with a ram attack on the same turn, the target takes an extra 7 (2d6) damage. If the target is a creature, it must succeed on a DC 16 Strength saving throw or be knocked prone.

Water Breathing. The Awakened Giant Nautilus can breathe only underwater.

Ram. Melee Weapon Attack: +5 to hit, reach 5 ft., one target. Hit: 6 (1d6 + 3) bludgeoning damage.

Tentacle. Melee Weapon Attack: +3 to hit, reach 10 ft., one target. Hit: 10 (2d6 + 3) bludgeoning damage. If the target is a creature, it is grappled(escape DC 16). Until this grapple ends, the target is restrained, and the Nautilus can't use its tentacles on another target.