Vigilant. The shark can't be surprised.

Transluscent. Due to the ghostly nature the shark has advantage on hiding, and stealth ability checks. 

Permeable. Due to the ghostly nature of the shark it has advantage on all ability checks against being grappled, or restrained.

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

Ectoplasmic Distribution (3/Day). The spiritual elements of the shark allow it to siphon off the souls of the nearly departed. It can repair 2d8 +  5 points to itself when a nearby creature within 30 feet that it can see dies.

Multiattack. The shark makes two attacks: one with it's bite and one with it's tail.

Bite. Melee Weapon Attack: +8 to hit, reach 5 ft., one target. Hit: 15 (2d8 + 4) piercing damage.

Tail Slam. Melee Weapon Attack: +8 to hit, reach 5 ft., one target. Hit: 19 (2d10 +4) bludgeoning damage.

Gale Force (Recharge 4-6). Ranged Weapon Attack: +7 to hit, reach 20-foot cone. Hit: 25 (4d10 + 2)

Spectral Shift. Once per round on any turn the Spectral Shark can reappear at the side of the one who summoned it.

Blood in the Water. When a creature within 5 feet of the shark makes an attack against a target other than the shark, it can use this reaction to make a melee weapon attack against the creature. If the attack succeeds the creature has disadvantage on it's attack roll, and it's movement speed is 0 for the remainder of the turn.