Valley of the Brain Collectors as a sandbox had plenty of optional encounters. However my players are very focused, it didn’t make sense to their practical hearted characters to disturb every nest in the Scar of the Spider. They stayed on mission. So they actually minimised and avoided contact with the inhabitants totally skipping the Cthulhu Mythos inhabited Fungal Cave. Here are the Mi-Go with the Pathfinder original here. One of the more interesting alien races from Lovecraft. The item creation special ability I couldn’t really convert to my satisfaction. 5e doesn’t make a big deal about item creation but since the Mi-Go do make strange tech-magic items I decided to leave it in with only slight modification.
An “advanced” Mi-Go appeared in the adventure as well. I just renamed them as Bodyguard Mi-Go and increased the various stats to that of a CR 7 monster per DMG pg. 273. They are otherwise identical to this monstrosity.
MI-GO 
Medium Plant, neutral evil
Armor Class 15 (natural armor)
Hit Points 168 (13d8 + 65)
Speed 30ft., fly 60 ft.
STR 16 (+2) DEX 20 (+5) CON 21 (+5)
INT 25 (+7) WIS 14 (+2) CHA 15 (+2)
Saving Throws Dex +5, Wis +5
Skills Perception +5, Bluff +7, Disguise +7, Heal +7
Damage Resistances fire, lightning; bludgeoning, piercing
Damage Immunities cold
Condition Immunities blinded, deafened, frightened
Senses blindsight 10ft., darkvision 120ft., passive Perception
Languages Telepathy 60 feet. Don’t speak though there is a humming sound when they use telepathy.
Challenge 6 (2,300 XP)
Deceptive. A mi-go is a master of deception. It has advantage on Bluff and Disguise checks. Bluff and Disguise are always class skills for a mi-go.
Evisceration (1/Turn). A mi-go’s claws are capable of swiftly and painfully performing surgical operations upon helpless creatures or those it has grappled. When a mi-go makes a successful grapple check, in addition to any other effects caused by a successful grapple, it deals sneak attack damage to the victim. The mi-go deals an extra 13 (4d6) damage when it hits a target that is grappled or helpless with an attack.
Tech-Magic. A mi-go possesses the ability to create strange items that blur the line between magic and technology, given time and resources. This ability allows a mi-go to ignore any prerequisite skill ore feat requirements and spellcasting requirements for creating a magic item; the resulting item is always mi-go technology. A mi-go can use the Medicine skill to craft mi-go technology. When a mi-go uses this ability to craft an item, it must use a larger amount of strange ingredients and expendable resources — this effectively doubles the gp cost to create the item.
Starflight. A mi-go can survive in the void of outer space. It flies through space at incredible speeds. Although exact travel times vary, a trip within a single solar system normally takes 3d20 months, while a trip beyond normally takes 3d20 years (or more, at the DM’s discretion)—provided the mi-go knows the way to its destination.
ACTIONS
Multiattack. The mi-go makes four claw attacks.
Claw. Melee Natural Weapon Attack: +8 to hit, reach 5 ft.; one target.
Hit: 19 (4d6 + 5) piercing damage plus target is grappled. Escape DC is 15 vs. Strength (Athletics) or Dexterity (Acrobatics).
DESCRIPTION
This unnaturally graceful creature has a bulbous fungoid lump for a head, spiny insectoid wings, and a tangle of spiky, clawed legs.
Your write up is suitably creepy.
Thank you kindly. A shame they didn’t see battle.