Moonshark

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

The shark can breathe only underwater.

A character within 5 feet of the shark can use an action to try to dislodge the spear, doing so with a successful DC 13 Strength (Athletics) check. While the spear is lodged in the shark, the shark glows with silvery illumination, shedding bright light in a 10-foot radius and dim light for an additional 10 feet.

Melee Weapon Attack +9 to hit, reach 5 ft., one target. 22 (3d10 + 6) Piercing damage. If the shark misses, it can use a bonus action to swim up to 25 feet. This movement doesn't provoke opportunity attacks.