Megalodon

Actions

Multiattack: The megalodon makes 3 bite attacks   Bite: Melee weapon attack: +13 to hit, reach 5ft., one target. Hit: 40 (6d10+7) piercing damage. Any creature that's hit by this attack and of the huge or smaller size is swallowed (escape DC 22). The swallowed creature is blind, restrained, and takes 18 (4d8) acid damage at the beginning of each of the megalodon's turns. The megalodon can have up to 9 medium or smaller creatures, two large creatures, or one huge creature swallowed at a time.   Ram: Melee weapon attack: +13 to hit, reach 5ft., one target. Hit: 45 (7d10+7) bludgeoning damage damage. All creatures on an object the megalodon hits with this attack must make a Constitution Saving throw (DC 22) or be shoved 30ft away from the megalodon. The creature has advantage on the saving throw if it can grab onto an object that's stationary. 

Megalodon is a well known beast roaming the waters. It's best described as a large shark. The Sahuagin revere these massive creatures as the children of a god, and worship them in turn.

Underwater