An Avengers: Endgame fan theory speculates Thanos (Josh Brolin), having fulfilled his mission in Avengers: Infinity War, is truly retired and the real villain will be a past version of the Mad Titan glimpsed in the credits tag of 2012's The Avengers.
Reddit user u/ak2sup shared the theory on the r/FanTheories subreddit, making a case for Endgame pitting Earth's mightiest heroes against a Thanos not yet in possession of the six Infinity Stones he used to annihilate fifty percent of all life in the universe come Infinity War.
The user questions why Thanos would withdraw from his peaceful retirement after having achieved his goal, writing instead a "more evil version," wielding only a double-bladed sword and his Chitauri army, will act as the leading villain after the last-surviving heroes travel back to the past — specifically the Battle of New York, where the Avengers first came together to ward off Thanos' invasion.
The theory continues to speculate the heroes will be forced to somehow utilize time travel to return to the past and collect the Infinity Stones, thus playing cosmic keep-away from Thanos in the future, but the user notes such a play could damage the timeline or result in an alternate timeline, potentially with damning results.
In another suggestion, the heroes return to the events of The Avengers and kill Thanos long before he ever makes his disastrous visit to Earth — a move that would wholly eradicate the events of Infinity War, thus reversing the decimation and returning the fifty percent of killed souls to life.
Such a plan would involve Tony Stark (Robert Downey Jr.) and Ant-Man (Paul Rudd) teaming to steal the Infinity Stone-powered scepter from minion Loki (Tom Hiddleston) before teaming with the Steve Rogers (Chris Evans) and Hulk (Mark Ruffalo) of the past to battle Thanos and his Black Order.
What the theory neglects to mention is Thanos could be drawn out of his quiet life as a farmer not because his mission is not yet complete, but because the Avengers are rallying to assemble and work to undo the snap — thus unraveling the victory Thanos worked years to achieve.
This theory appears to be inspired by spoilery set photos captured in late 2017, showing Evans, Downey, Ruffalo and Rudd filming scenes in a revisit to the Battle of New York. Also present was Hiddleston's captured Loki, with the characters boasting both familiar yet different looks — indicating obvious time hopping hijinks.
Avengers: Endgame opens April 26.