#5. Tony Stark's Arc Reactor Uses Infinity Stone Energy
In the memorable scene in Marvel's The Avengers when Loki attempts to use his scepter (which we now know houses the mind gem, thanks to Age of Ultron) to hypnotize Tony Stark, he noticeably fails, with Stark spouting out statistics about performance issues (1 out of 5. . .). Although many audiences have concluded that Loki fails because the scepter simply did not make contact with Stark's body, som fans have a deeper theory.
Some have reasoned that when Stark creates the "new element" that powers his arc reactor in Iron Man 2, he actually created energy that already existed within the Infinity Stones, and it only seemed "new" because it was alien to Earth. This would explain why Loki's scepter had no effect on him, since Stark's body is already accustomed to the unique energy.
#4. Janet Van Dyne becomes Eternity
Although Wasp only appears in Marvel's Ant-Man for a short scene (and an end credits scene), she plays quite a large role in the film, providing a source of angst for Hank Pym, as well as a reason for separation between him and his daughter Hope. Said scene sees Wasp sacrifice herself in order to stop a Russian missile, turning off her regulator in order to shrink between the molecules of the weapon and disable it. She then ends up in the Quantum Realm (known as the Microverse in the comics), unable to escape, something that Scott Lang manages later in the film. When Scott returns to our world, he remembers nothing about his trip to the Quantum Realm, and Hank suggests that the human mind simply cannot comprehend the experience.
However, if Janet was trapped there for years, decades even, while fully aware of the experience, her brain could have evolved in order to understand the unique properties of the dimension, making her a more powerful being in the Quantum Realm. Moviegoers have reported seeing a silhouette in the Quantum Realm, while Hank Pym repeatedly utters the word "eternity". Could Janet Van Dyne have become the force of the universe known as Eternity?
#3. Deadpool will Remember Two Lives
Let's take a break from the Marvel Cinematic Universe for a bit and discuss fan-favorite Deadpool. Due to his long awaited solo movie set to drop next year, many fans have developed theories for his involvment in the X-Men Cinematic Universe (XCU?). One of these theories states that Deadpool will remember two lives in his film next year. At the end of X-Men Origins: Wolverine, those who soldiered through the credits (and the rest of the movie) are rewarded with a sneak peak of Deadpool's future in the XCU, seeing him break the fourth wall and look directly into the camera, with a quiet "shh".
Several fans think that, after Wolverine reset the timeline in Days of Future Past, Deadpool retained his memory of the original XCU, as well as his new life in the reset universe. This could contribute to his apparent insanity that we'll see in Deadpool's solo movie; plus, if he knows about the original XCU, who says he doesn't know about OUR universe, explaining his habit of constantly breaking the fourth wall.
#2. There are Two Infinity Gauntlets
In the mid-credits scene of Avengers: Age of Ultron, we see Thanos opening a vault and putting on an Infinity Gauntlet (void of all gems) and declaring "fine, I'll do it myself", clearly referring to how Loki failed to bring him the Tesseract (space gem) in The Avengers, and Ronan's failure to bring him the Orb (power gem) in Gaurdians of the Galaxy. However, eagle-eyed viewers will remember that we actually saw the Infinity Gauntlet once before in Odin's vault, in Thor.
Well, one theory states that after Loki's failure to obtain the Tesseract for Thanos, he made it up to him by stealing the Infinity Gauntlet from Odin's vault, giving it to Thanos, and replacing the original with a fraud (he is a trickster, after all). This could all be a part of Loki's grand scheme to let Thanos do all the work and then take the Infinity Gauntlet for himself (with all the gems), which is something that happened in the comics (but not with Loki).
Then again, the gauntlet we see in Thor is for a right hand, while the one at the end of AOU was for a left hand, so maybe Thanos just made the Infinity Gauntlet himself (and maybe Adam Warlock will use the other one in Infinity War?).
#1. The Identity of Jared Leto's Joker
Alright Marvel, you've had your fun, give DC a turn. This is a popular theory that you may have heard before, but I couldn't make this list without it. Simply put, Jared Leto's joker is none other than Jason Todd. For those of you who aren't familiar with the "Death in the Family" storyline, the Joker beats Jason Todd (the first Robin) to death with a crowbar, but in "Under the Red Hood", it is revealed that he is still alive, now under the vigilante alias (you guessed it!) the Red Hood (in Rocksteady's Batman: Arkham Knight, Jason becomes the Arkham Knight, and attempts to extract his revenge upon Batman for abandoning him).
In DC's upcoming Suicide Squad, Jason Todd could take on another alias, this time becoming none other than the Joker. In the official trailer for the Suicide Squad, we see that the tattoo on Jared Leto's face is not a teardrop, as some people suspected, but it is in fact a "J". Sure this could stand for "Joker", but it could also be a brand that the original Joker gave Jason Todd, for "Jason" (something similar is seen in Arkham Knight). If Jason Todd was the Joker, he would also know Batman's secret identity, explaining how he knew that Wayne Tower was Batman's, and was able to taunt him in the Batman V Superman Comic-Con trailer, saying "you let your family die" (referring to either Bruce Wayne's parents or Robin).
Just kidding, actual bonus theory:
Since it is revealed that Ant-Man and Wasp were both agents of Shield in the 1980s, perhaps they had some involvment in the creation of the Avenger Initiative (introduced in Iron Man), and maybe Wasp came up with the name "Avenger", just as she does in the comics.
Maybe? . .