Crystal Bound Giant Shark

Blood Frenzy. The shark has advantage on melee attack rolls against any creature that doesn't have all its hit points.

Water Breathing. The shark can breathe only underwater.

Acid Shroud. Each creature that starts or ends its turn within 5 feet of the giant shark must make a Constitution check of 18 or take 2d6 acid damage on a failed save or half as much on a successful check.

Crystal Bound. The giant shark can not betray the bearer of it's crystal powers, thus is immune to effects that would allow it to attack or interact differently towards Crystals Druids or Crystal Soldiers.

Crystal Power. Magical power that comes from crystals forming unnaturally on the body of the host. This power can vary based on what plane it comes from. (This can be changed up to the DM's requirements)

Multiattack. The giant shark makes two attacks, one with its bite and one with tail swipe.

Bite. Melee Weapon Attack: +9 to hit, reach 5 ft., one target. Hit: 22 (3d10 + 6) piercing damage and 1d8 acid damage.

Tail Swipe. Melee Weapon Attack: +9 to hit, reach 10 ft., one target. Hit: 1d8 + 6 bludgeoning damage and 1d8 acid damage.

Crystal Bubble (Recharge 5-6). Roll 1d4 and create that many bubbles of acid. The bubbles have an AC of 5 and 10 hp, they explode at the end of the giant sharks next turn or when destroyed. Each creature within 10 feet of an exploding acid bubble must make a Dexterity saving throw DC 17 or take 4d8 acid damage on a failed save or half as much on a successful save.