Statue’s Guise (Quantum Lock). While being observed by a conscious creature, the Infernal Watcher becomes petrified (as if under the petrified condition), appearing as a mundane statue. While petrified in this way, it cannot be harmed or moved except by magical means such as disintegrate.

Unseen Predator. The Watcher has advantage on attack rolls against creatures that cannot see it (including those who are blinded, looking away, or have their eyes closed).

Infernal Grasp. A creature hit by the Watcher’s Slam must succeed on a DC 16 Charisma saving throw or be magically frozen in place, locked in a psychic struggle against the Watcher’s will. While frozen, the creature is incapacitated and restrained but remains aware of its surroundings. At the end of each of its turns, it can make another Charisma saving throw, ending the effect on a success.

Multiattack. The Watcher can make two Slam attacks.  But only if unobserved.

Slam. Melee Attack Roll: +9, reach 5 ft. Hit: 17 (2d10 + 6) Bludgeoning damage.

Horrific Advance. The Watcher magically teleports up to 30 feet to an unoccupied space it can see, provided no conscious creature can see it move. This does not provoke opportunity attacks.

Frozen Terror (Recharge 5–6). Each creature within 30 feet that can see the Watcher must succeed on a DC 16 Wisdom saving throw or be frightened until the start of the Watcher’s next turn.