False Appearance. While the yowler remains motionless, it is indistinguishable from a wooden barrel or other container. Looking inside reveals the yowler's true nature.

Multiattack. The yowler makes two bite attacks.

Bite. Melee Weapon Attack: +9 to hit, reach 10 ft., one creature. Hit: 21 (5d6 + 4) piercing damage.

Multiply. The yowler magically creates 1d10 illusory copies of itself within 60 feet. The copy cannot be determined as an illusion by physical interaction. A creature can use its action to determine if a copy is an illusion with an Intelligence(investigation) check (DC 20). The yowler and the copies attack in unison, but only the yowler's attacks have an effect. 

A copy uses the yowler's AC and uses its saving throws. If an attack hits a copy, or if a copy fails a saving throw against an effect that deals damage, the copy disappears. When the yowler uses this action, it can teleport to trade places with a copy as a bonus action. A yowler can only have 10 copies at one time.

Replace. If the yowler takes any damage, it can teleport to trade places with a copy if a copy is within 60 feet of the yowler.

The yowler can take 3 legendary actions, choosing from the options below. Only one legendary action option can be used at a time and only at the end of another creature’s turn. The yowler regains spent legendary actions at the start of its turn.

Bite. The yowler makes one bite attack.

Swap. The yowler teleports to trade places with a copy within 60 feet of the yowler.

Yowl (Costs 3 Actions). The yowler lets out a long baleful scream. Each creature within 15 feet of the yowler or its copies must make a DC 19 Constitution saving throw, taking 40 (9d8) thunder damage on a failed save or half as much on a successful one. If a creature fails by 10 or more, they become deafened until cured.