Giant Water Scorpion

Hold Breath. The scorpion can hold its breath for 1 hour. If it is within 15 feet of the water's surface, it can use its tail as a breathing tube and doesn't need to hold its breath.

Poison Injection. When the scorpion hits with a proboscis attack against a grappled, paralyzed, restrained, or stunned creature, it deals an extra 10 (3d6) poison damage.

Underwater Camouflage. The scorpion has advantage on Dexterity (Stealth) checks made to hide while underwater.

Multiattack. The giant water scorpion makes two claw attacks. If it is grappling a creature, it can use its proboscis once.

Proboscis. Melee Weapon Attack: +5 to hit, reach 5 ft., one target. Hit: 8 (1d10 + 3) piercing damage, and the target's Strength score is reduced by 1d4. The target dies if this reduces its Strength to 0. Otherwise, the reduction lasts until the target finishes a short or long rest.

Claws. Melee Weapon Attack: +5 to hit, reach 10 ft., one target. Hit: 6 (1d6 + 3) piercing damage. The target is grappled (escape DC 13) if it is a Medium or smaller creature and the scorpion doesn't have another creature grappled.