Bunyip

Amphibious. The bunyip can breathe air and fresh water.

Disease Immunity. The bunyip is immune to disease, and cannot be affected by spells or effects that bestow disease.

Fearsome Appearance. When creatures within 60ft see the bunyip for the first time, they must make a DC 19 Charisma saving throw; on a failure, the creature is afraid of the bunyip; it can make the saving throw again at the end of each of its subsequent turns to break the fear effect. On success, the creature is immune to the bunyip's Fearsome Appearance for the next 24 hours.

Jaw Lock. When the bunyip makes a successful bite attack, the target of its attack is considered grappled.

Fresh Water Dependency. The bunyip takes 12 (2d12) acid damage every hour it goes without being immersed in fresh water, or every minute it is submerged in salt water.

Death Roll. If the bunyip starts its round with a grappled creature, it can take the disengage action to drag the grappled creature into the water (Contested Strength check). When a creature grappled by the bunyip enters the water, it can hold its breath for 1d4 + CON modifier rounds before it starts to drown.

Water Surge. If the bunyip begins and ends its turn in water, its movement speed is doubled for that turn.

Multiattack. The bunyip makes two attacks, one with its claws and one bite attack. If the bunyip has a creature grappled, it can instead make two claw attacks to the grappled creature.

Claw. Melee Weapon Attack: +7 to hit, reach 10 ft., 1 target. Hit: 10 (2d6 + 4) slashing damage. 

Bite. Melee Weapon Attack: +7 to hit, reach 5 ft., 1 target. Hit: 16 (2d12 + 4) piercing damage. When the bunyip makes a successful bite attack, the target of its attack is considered grappled. A DC 17 Strength or Dexterity check is required to break the grapple.