One of the things we learned in our extensive look at Stranger ThingsDemogorgon concept art was just how much engineers thought to realize the creature practically. Now, gruesome behind-the-scenes photos and videos from production show just how the Upside Down monster looked as a terrifying physical effect.

After Stranger Things creators Matt and Ross Duffer recruited concept artist Aaron Sims to finalize a Demogorgon design, Spectral Motion stepped in to build both a costume for on-set performers, and an animatronic head. The company now shares a look at that practical effects work, to keep you awake well-past midnight:

Contortionist Mark Steger served as the on-set actor for the Demogorgon, while Aaron Sims told us of the practical effects:

The creature was designed so that we wouldn’t limit ourselves to only using the actor in his suit, but it still had to be humanoid and relatable. We actually went through the process of reverse-engineering the way the actor could wear it as a suit, where it looked like the monster with some slight CG enhancements from us. Mark Steger, the contortionist who actually wore the suit, had to be thin enough to capture that creepy look.

The use of full CG was more related to when an actor in a suit couldn’t perform certain stunts - especially when we had supernatural elements, like the Demogorgon breaking through walls. We had to show another world reaching into ours, and those shots had to be fully VFX.

In the meantime, it isn’t clear if we’ll see the Demogorgon (as opposed to new creatures) in Stranger Things Season 2, but stay tuned for more as we head into 2017.

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