Innate Spellcasting. The Night Queens innate spellcasting ability is Intelligence (spell save DC 18, +10 to hit with spell attacks). She can innately cast the following spells, requiring no material components: At will: detect magic, Eldritch Blast, ray of enfeeblement, sleep, detect evil and good, detect thoughts 

5/day each: Bane, protection from poison, sanctuary, shield

1/day each: dream, scrying

Magic Weapons. The Night Queen's weapon attacks are magical.

Shielded Mind. The Night Queen's is immune to scrying and to any effect that would sense its emotions, read its thoughts, or detect its location.

Multiattack: The Night Queen makes two attacks with its Dark Rags .

Dark Rags: Melee Weapon Attack: +10 to hit, reach 15 ft., one target. Hit: 11 (2d6 + 4) slashing damage. The target is Grappled (escape DC 16) if the Night Queen isn't already Grappling a creature. Until this grapple ends, the target is Restrained and takes 7 (2d6) piercing damage at the start of each of its turns.

Animate Dark Rags: As an action The Night Queen can animate four Dark Rags. 
Each Dark Rags is an object with AC 20, 20 Hit Points, Resistance to piercing damage, and immunity to psychic and thunder damage. When the devil uses Multiattack on its turn, it can use each animated Dark Rags to make one additional Dark Rags Attack. An animated Dark Rags can grapple one creature of its own but can't make attacks while Grappling. An animated Dark Rags reverts to its inanimate state if reduced to 0 Hit Points or if the devil is Incapacitated or dies.

Teleport (Recharge 2): The The Night Queen magically teleports, along with any Equipment it is wearing or carrying, up to 40 ft. to an unoccupied space it can see. 

Change Shape. The Night Queen magically polymorphs into a  beast that has a challenge rating equal to or less than its own, or back into its true form. It reverts to its true form if it dies. Any equipment it is wearing or carrying is absorbed or borne by the new form.

In a new form, the couatl retains its game statistics and ability to speak, but its AC, movement modes, Strength, Dexterity, and other actions are replaced by those of the new form, and it gains any statistics and capabilities (except class features, legendary actions, and lair actions) that the new form has but that it lacks. 

Can take 3 Legendary Actions, choosing from the options below. Only one legendary action can be used at a time, and only at the end of another creature's turn. Spent legendary Actions are regained at the start of each turn.

Cast: The Night Queen casts a spell 

Legendary Resistance (3/Day). If the Night Queen fails a saving throw, it can choose to succeed instead.

Curse of the Toad:  The Night queen can curse a player and turn them into a Toad. The player makes a DC 18 Con save or becomes a Giant Toad. Only one player can be a  toad at a time. The Player can make another Con save at the end of its turn to resist the curse.