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.

Pack Tactics. The Zombie Shark has advantage on an attack roll if at least one of the Zombie Shark's allies is within 5 feet of the creature and the ally isn't incapacitated.

Undead Fortitude. If damage reduces the zombie to 0 hit points, it must make a Constitution saving throw with a DC of 5 + the damage taken, unless the damage is radiant or from a critical hit. On a success, the zombie drops to 1 hit point instead.

Bite. Melee Weapon Attack: +6 to hit, reach 5 ft., one target. Hit: 13 (2d8 + 4) piercing damage plus 5 (2d4) Necrotic damage.