Warlock of the Great Old One, Legendary

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

Whispering Aura. At the start of each of the warlock’s turns, each creature of its choice within 10 feet of it must succeed on a DC 17 Wisdom saving throw or take 10 (3d6) psychic damage, provided the warlock isn’t incapacitated.

Multiattack. The warlock makes two Dagger attacks.

Dagger. Melee or Ranged Weapon Attack: +7 to hit, reach 5 ft. or range 20/60 ft., one target. Hit: 5 (1d4 + 3) piercing damage plus 10 (3d6) psychic damage.

Innate Spellcasting. The Warlock's innate spellcasting ability is Charisma. It can innately cast the following spells (spell save 17), requiring no material components:

At will: detect magic, mind sliver(3d6), levitate, mage armor (self only), mage hand, minor illusion, prestidigitation, speak with dead, eldritch blast (3 beams, 1d10 +4),

1/day each: arcane gate, detect thoughts, power word pain, maddening darkness

Howling Void. The warlock opens a momentary extraplanar rift within 60 feet of it. The rift is a scream-filled, 20-foot cube. Each creature in that area must make a DC 15 Wisdom saving throw. On a failed save, a creature takes 9 (2d8) psychic damage and is frightened of the warlock until the start of the warlock’s next turn. On a successful save, a creature takes half as much damage and isn’t frightened.

The Warlock can take 3 Legendary actions, choosing form 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 warlock regains spent Legendary actions at the Start of its Turn. 

Move. The warlock moves up to half its speed without provoking opportunity attacks.
Cantrip. The warlock casts a cantrip.
Dagger. The warlock attacks with its Dagger.
Mouth of Madness (Costs 1-3 Actions). The warlock utters an unworldly phrase and targets up to 3 creatures it can see within 30 feet of it. If the target can see and hear the warlock, it must succeed on a DC 17 Wisdom saving throw. On a failed save, the target must use its reaction to move up to half its speed toward a creature of the warlock's choice that it can see and make one melee weapon attack against it, if it is within range.
It costs 1 legendary action per target.