Amulet of the Spectral Shark

While wearing this amulet you gain a shark like appearance and gain the ability water breathing and a 30 foot swim speed. You also can summon a special shark once per long rest. 

Spectral Shark. You can summon a ghostly shark as a faithful companion that is friendly to you and your allies, and obeys your commands. See the creature's game statistics in the Spectral Shark stat block, if your proficiency bonus (PB) surpasses the shark's you may add yours instead. In combat, the spectral shark shares your initiative count, but takes its turn immediately after yours. It can move and use its reaction on its own, but the only action it takes on its turn is the Dodge action, unless you take a bonus action on your turn to command it to take another action. That action can be one in its stat block or some other action. If you are incapacitated, the creature can take any action of its choice, not just Dodge.

If the mending spell is cast on it, it regains 2d6 hit points. If it has died within the last hour, you can expend a spell slot of 1st level or higher as an action to revive it; or you may use any crafting tools you have proficiency with, provided you are within 5 feet of it. The spectral shark returns to life after 1 minute with all its hit points restored.

At the end of a long rest you can summon a new Spectral Shark. If you already have a spectral shark the original dies. The shark also dies if you die.

SPECTRAL SHARK: Medium Construct

Armor Class: 15 Natural Armor
Hit Points: 50 (8d10)
Speed: 0 ft., swim 60 ft., Flight 45 ft. (hover)

STR:17 (+3)  DEX: 14 (+2)  CON: 16 (+3)  INT: 4 (-3)  WIS: 6 (-2)  CHA: 10 (+0)

Saving Throws: DEX +7, CON +8
Damage Vulnerabilities: Radiant
Damage Resistances: Necrotic, Bludgeoning from non magical attacks
Condition Immunities: Charmed, Exhaustion, Frightened
Senses: Blindsight. The shark can see while blinded within 10 feet as long as the creature within range is below max HP., Passive Perception 12
Languages: It can understand any language of the one that summoned it understands.
Challenge -- Proficiency Bonus of the summoner

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.

Actions
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: 3 + proficiency bonus to hit, reach 5 ft., one target. Hit: 15 (1d8 + 3) piercing damage.

Tail Slam. Melee Weapon Attack: 3 + proficiency bonus to hit, reach 5 ft., one target. Hit: 19 (1d10 +3) bludgeoning damage.

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

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

Reactions
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.

Description
This ghostly shark is a spirit of the storm. Brought back to this realm through a tornado and the cry of sharks. When slain it leaves behind a piece of itself, so it never truly dies.

Notes: spellcaster, or someone proficient with crafting tools.