Agents of SHIELD officially has a monster problem, on earth and in outer space.

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Coulson (Clark Gregg) and Co. know what they're dealing with when it comes to the Inhumans, but Fitz (Iain De Caestecker), Simmons (Elizabeth Henstridge), and the audience are completely at a loss when it comes to whatever nefarious creature hounded Simmons and Will (Dillon Casey) on the other side of the portal. While SHIELD searches for answers, we've compiled the best clues and theories from the cast, crew, and beyond.

The Agents' Take

Henstridge took on her biggest episode to date with "4,722 Hours," but the aftermath of Simmons' unintentional vacation has furnished viewers with a few new teasers.

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"We'll learn more about that. It will have an impact going forward," Henstridge said of the mysterious sand-shrouded menace. The actress also weighed in on the creature's worrisome shape shifting skills. "How we're setting it up is it manipulates you and uses what will sway you. It wanted Simmons to think that NASA had come back so that she would go toward it."

As to where the monster calls home, well, it may not be a planet Marvelites have ever seen. When fans asked VFX supervisor Mark Kolpack why the world looks like nothing from Marvel canon, he informed them it is "because we made it up."

The Best From The Rest

Far and away, the best fan theories we've seen have come from Comic Book Resources. The sire recently posited that Simmons home away from home could be Ego the Living Planet. While this flies in the face of Kolpack's statement, there is incredibly sound reasoning behind the idea.

Will is convinced the planet has "moods." Ego does have moods. From a paradise that would make the Hanging Gardens of Babylon look like child's play to the desert wasteland Simmons encountered, Ego can control his size and environs. In addition, he absorbs travelers and, if there is a problem doing so, his antibodies jump into action. Is sandstorm man an antibody?

Comic Book Resources also forwarded the idea that the creature could be a Dire Wraiths. Mostly this intrigues us due to the wraiths connections to the Inhumans (they were experimented on by the Kree) and darkforce. Agent Carter will dive into darkforce this winter, and Agents of SHIELD could easily capitalize on the series' exposition.

What do you think? Find out more when Agents of SHIELD airs Tuesdays at 9 p.m. ET on ABC.

Tags: Marvel's Agents of S.H.I.E.L.D. television ABC Marvel