Undead Nature. The Yowler doesn't require air, food, drink, or sleep.

Living Projection. The yowler's undead form is constantly covered with a magical illusion that makes it look like it did in life. This effect is suppressed for 1 minute if the yowler attacks or uses Yowl.
The changes wrought by this illusion fail to hold up on physical inspection. For example, the yowler's fur appears soft and silky, but someone touching it would feel the yowler's rotten fur and exposed bones. Otherwise, a creature must take an action to visually inspect the illusion and succeed on a DC15 Intelligence (Investigation) check to discern the yowler's true appearance. 

Multiattack. The Yowler makes two attacks: one with its bite, and one with its claws. It can use Yowl in place of a bite attack.

Bite. Melee Weapon Attack: +4 to hit, reach 5 ft., one target. Hit: 4 (1d4 + 2) piercing damage, and the target must succeed on a DC12 Constitution saving throw or be poisoned until the end of its next turn. 

Claws. Melee Weapon Attack: +4 to hit, reach 5 ft., one target. Hit: 5 (1d6 + 2) slashing damage. 

Yowl. The yowler lets loose a horrid scream. Each hostile creature within 30ft of the yowler that can hear it must succeed on a DC12 Wisdom Saving Throw or become frightened for1 minute. A creature can repeat the saving throw at the end of each of its turns, ending the effect on itself on a success. If a creature's saving throw is successful or the effect ends for it, the creature is immune to the yowler's Yowl for the next 24 hours.