Chasme Queen

Drone. The chasme produces a horrid droning sound to which demons are immune. Any other creature that starts its turn within 30 feet of the chasme must succeed on a DC 16 Constitution saving throw or fall unconscious for 10 minutes. A creature that can’t hear the drone automatically succeeds on the save. The effect on the creature ends if it takes damage or if another creature takes an action to splash it with holy water. If a creature’s saving throw is successful or the effect ends for it, it is immune to the drone for the next 24 hours.

Magic Resistance. The chasme has advantage on saving throws against spells and other magical effects.

Spider Climb. The chasme can climb difficult surfaces, including upside down on ceilings, without needing to make an ability check.

Multiattack. The Chasme Queen makes three attacks: Two with its claws, one with its Proboscis.

Claw. Melee Weapon Attack: +8 to hit, reach 10 ft, one creature. Hit: 13 (2d6+6) piercing damage plus 14 (4d6) necrotic damage.

Proboscis. Melee Weapon Attack: +8 to hit, reach 10 ft., one creature. Hit: 27 (6d6 + 6) piercing damage plus 28 (8d6) necrotic damage, and the target’s hit point maximum is reduced by an amount equal to the necrotic damage taken. If this effect reduces a creature’s hit point maximum to 0, the creature dies. This reduction to a creature’s hit point maximum lasts until the creature finishes a long rest or until it is affected by a spell like greater restoration.

Summon Demon (1/Day). The demon chooses what to summon and attempts a magical summoning.

A chasme queen has a 100 percent chance of summoning 1d6 chasme.

A summoned demon appears in an unoccupied space within 60 feet of its summoner, acts as an ally of its summoner, and can’t summon other demons. It remains for 1 minute, until it or its summoner dies, or until its summoner dismisses it as an action.

The Demon 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 Demon regains spent legendary actions at the start of its turn.

Detect. The Chasme Queen makes a Wisdom (Perception) check.

Claw. The Chasme Queen makes one claw attack

Wing Attack (Costs 2 Actions). Chasme Queen beats his wings. Each creature within 15 feet of Chasme Queen must succeed on a DC 16 Dexterity saving throw or take 13 (2d6 + 6) bludgeoning damage and be knocked prone. Chasme Queen can then fly up to half her flying speed.