Whistler

Attack rolls against the whistler are made with disadvantage unless the whistler is incapacitated.

The whistler doesn't require air, food, drink, or sleep.

The whistler makes three Psychic Swipe attacks.

Melee Spell Attack: +8 to hit, reach 10 ft., one creature. Hit: 15 (2d10 + 4) psychic damage.

The whistler telepathically whistles an otherworldly melody into the minds of up to two creatures it can see within range of its telepathy. Each target must succeed on a DC 16 Wisdom saving throw or take 33 (6d10) psychic damage and become frightened of the whistler for 1 minute. A frightened creature can repeat this saving throw at the end of each of its turns, ending the effect on itself on a success.

The whistler teleports up to 20 feet to an unoccupied space it can see.