Dacre Montgomery lobbied the Duffer brothers (Matt Duffer & Ross Duffer) for the scene between Billy and his father, Neil Hargrove (Will Chase), saying that "I can't just play bad, because nobody's just bad."
The title refers to a species of very powerful creatures in Dungeons and Dragons. Mindflayers come from the same mythos as Cthulu and are tentacled-faced beings who can "suck" the minds out of their victims as a form of sustenance.
Originally titled "The Brain".
The episode won an Emmy Award for Outstanding Sound Editing for a Comedy or Drama Series (One Hour).
Dustin's (Gaten Matarazzo) example for skin shedding is hornworm. While hookworms, tapeworms, pinworms, and flatworms are nasty intestinal parasites hornworms are the caterpillars of hawk moths (over 1,400 species of hawk moth). Dustin might have thought of that critter before any other of the over 800,000 species of critters on Earth that molt because of lost and forgotten Yurtle. Hornworms are raised and sold in pet stores as turtle and lizard food.