Bob the Giant Platypus

Electroreception. Specialised nerve endings in the bill of the giant
platypus detect the electrical currents generated by the muscle
contractions of its prey, allowing it to sense the presence of all
creatures within a 1 mile radius that are in the same body of
water. The giant platypus does not need to be able to see or hear
for this to take effect.

Hold Breath. The giant platypus can hold its breath for 30
minutes

Aquatic Mammal. While the giant platypus is on land it has
disadvantage on dexterity checks and saving throws.

Bite. Melee Attack Roll: +6, reach 5 ft. Hit: 5 (2d10 + 4) Piercing damage. If the target is a Medium or smaller creature, it has the Grappled condition (escape DC 13). Until this grapple ends, the target is Restrained, and the giant platypus can't bite another target. If the target creature is paralyzed the giant platypus can instead choose to replace this bite attack with the swallow action.

Swallow. The giant platypus swallows a Medium or smaller target it is grappling into the platypus's cheek pouch, which is filled with sharp stones and gravel, and the grapple ends. The swallowed target is restrained, it has total cover against attacks and other effects outside the giant platypus, and it takes 10 (3d6) Acid damage at the start of each of the giant platypus's turns. The giant platypus can have only one target swallowed at a time.

If the giant platypus dies, a swallowed creature is no longer restrained by it and can escape from the corpse using 5 feet of Movement, exiting prone.

Sting. Melee Attack Roll: +6, reach 5 ft. Hit: 13 (2d8 + 4) Piercing damage plus 5 (1d10) Poison damage. the target must succeed on a DC 13 Constitution saving throw or be poisoned for 1 minute. Until this poison ends, the target is paralyzed. The target can repeat the saving throw at the end of each of its turns, ending the poison on itself on a success.