Booyahg Slave of the Great Old One

At the start of each of the goblin's turns, each creature of its choice within 5 feet of it must succeed on a DC 15 Wisdom saving throw or take 10 (3d6) psychic damage, provided that the warlock isn't incapacitated.

The goblin's innate spellcasting ability is Charisma. It can innately cast the following spells (spell save DC 15), requiring no material components:

At will: detect magic, jump, levitate, mage armor (self only), speak with dead

1/day each: arcane gate, true seeing

The goblin is a 14th-level spellcaster. Its spellcasting ability is Charisma (spell save DC 15, +7 to hit with spell attacks). It regains its expended spell slots when it finishes a short or long rest. It knows the following warlock spells:

Cantrips (at will): chill touch, eldritch blast, guidance, mage hand, minor illusion, prestidigitation, shocking grasp

Level 5 (3 slots): armor of Agathys, arms of Hadar, crown of madness, clairvoyance, contact other plane, detect thoughts, dimension door, dissonant whispers, dominate beast, telekinesis, vampiric touch

Melee or Ranged Weapon Attack: +5 to hit, reach 5 ft. or range 20/60 ft., one target. Hit: 4 (1d4 + 2) piercing damage.