Bedbug

Insomnisite. The bedbug can detect Unconscious creatures within a 1-mile radius. While within a dream, the bedbug can also choose to alter it's form to match it's surroundings. The new form can be of size Large or smaller. 

Magic Resistance. The bedbug has Advantage on saving throws against spells and other magical effects.

Sleepcasting. While the bedbug is within a dream, the bedbug casts one of the following spells, requiring no spell components and using Charisma as the spellcasting ability (spell save DC 15):

3/Day: fear (Nightmare Only), enhance ability (Daydream only), major image, nystul's magic aura

1/Day: creation (Daydream Only) mental prison (Nightmare Only), mirage arcane

Dreamsand. Wisdom Saving Throw: DC 15, each creature in a 15-foot cone. Failure: The target gains the Incapacitated condition until the end of its next turn, at which point it must repeat the save. If the target fails the second save, the target falls Unconscious for 10 minutes, or if it takes damage or someone within 5 feet of it takes an action to shake it. 

Sting (Nightmare Only). Melee Weapon Attack: +7 to hit, reach 5 ft., one target. Hit: 13 (2d8 + 4) Psychic damage, and the target has Disadvantage on the next saving throw it makes. 

Infect. Charisma Saving Throw: DC 15, a dreaming creature. Failure: The target's dream is implanted with a bedbug egg. The target is unaware of this implantation. If the target is dreaming pleasantly, the egg hatches into a Daydream bedbug. If the target's dream is tormenting the dreamer, a Nightmare bedbug hatches. 

Drift Off. Wisdom Saving Throw: DC 15, an Unconscious creature within 5ft. Failure: The bedbug vanishes from it's current plane and enters the targets dream. A protection from evil and good spell cast on the target prevents this contact, as does a magic circle. The bedbug can remain in the dream as long as the target remains alive, and the target remains Unconscious until the bedbug leaves the dream with another Bonus Action. 

Legendary Action Uses: 3. Immediately after another creature's turn, The bedbug can expend a use to take one of the following actions. The bedbug regains all expended uses at the start of each of its turns.

Metamorph (2 Actions). The bedbug casts a spell using it's Sleepcasting trait with a casting time of Action. 

Teleport. The bedbug magically teleports, up to 60 feet to an unoccupied space it can see.

Vanish. The bedbug magically becomes invisible for up to 10 minutes or until immediately after it makes an attack roll.