Agents of S.H.I.E.L.D. - Who or What is the Mysterious Evil?

Wraith

There have been many people in the Marvel universe called "Wraith," but one of those in particular is linked directly to the Kree, a character named Zak-Del. He's the son of a Kree scientist. He was banished to a barren planet (sound familiar?).

Now here's where we get a little creative - combine that back story with the alien race known as the Dire Wraiths, who are another shapeshifting, dark magic using race in the Marvel Universe. Now, they're a little tough, because we don't know if Marvel owns the film rights to those characters (they've had links to both Skrulls, who belong to Fox, and the X-Men, who belong to Fox), but it's intriguing. The Marvel Cinematic Universe has mixed and matched characters a bit before, so some combination of these could make a lot of sense.

Ebony Maw

"It's all connected," remember? That's the favorite three-word answer of Marvel TV head Jeph Loeb whenever asked about how the shows connect to each other, or how they connect to the films. Well, the film word is all moving, eventually, to Thanos. Unfortunately, that's a hard thing to tie-in to something like Agents of S.H.I.E.L.D. Unless, of course, you just go with one of Thanos's lieutenants.

Ebony Maw, one of the Mad Titan's "Black Order," is a character with psychological abilities, who has helped Thanos raze entire planets, and has multiple direct links to Inhumans (including manipulating Thanos's son Thane, on the left, who frankly is a bit of a possibility, too!). His connections there would certainly help the character make the connection; when we look at the Black Order, this is the one that would make the most sense, and they certainly have the ability to live the hundreds of years needed to be consistently killing human visitors since at least 200 years ago.

Conveniently, this character also has ties to Dr. Strange, so he'd really be great setup for the whole of MCU phase 3.

Death

Speaking of connections to Thanos, there's always the simple manifestation of Death, who can easily exhibit all of the abilities we described in the intro. The biggest problems here are being restricted to one place (um, people are still dying, after all), and the fact that Death really prefers manipulating people (like Thanos) into doing her bidding, rather than getting hands on and eating astronauts.

Another Out-There Cosmic Threat

Some quick one-liners and housekeeping guesses:

Beyonder - Because all MCU speculation (see: Star-Lord's MCU dad) has to include the Beyonder in it at least once. Why he'd be stuck on a desolate Kree planet we have no idea.

Nightmare - Connection to Dr. Strange, ability to psychically manipulate.

Mephisto - similar to above, and they did pointedly say that world was "hell."

Abraxas - Yeah, pretty sure this is considered a Fantastic Four villain, but he is the embodiment of destruction, and so he gets a brief mention.

Something Brand-New

Honestly, when you have the wealth of villainy in the Marvel Comics universe, it's hard to think they'd do something brand new, especially since the producers and writers of this show know, love, and have a fondness for showing off the worlds of Marvel Comics. But it's always a possibility.

The bigger probability is that they'll take something familiar from the comics, and tweak it to make it their own. EP Jeff Bell has said they do everything on the show for a reason and with a lot of thought behind it, so teasing a character like this then not paying it off just isn't going to happen. The bigger payoff for comic book fans is to have a version of a comic book character, and as the Inhumans and Daisy Johnson have shown, the Agents of S.H.I.E.L.D. creative team agrees with that whole-heartedly.