In Avengers: Infinity War, Thanos cut through swaths of heroes before wiping out half of all life in the universe with the snap of his fingers. He accomplished that with relative ease, opting for casual wear for much of the film, over battle armor. However, new toys and collectibles for Avengers: Endgame reveal Thanos with a double-edged blade, raising questions about why the owner of the Infinity Gauntlet needs such a weapon.
The blade isn't a gimmick to sell more toys; it's a legitimate part of Thanos' arsenal: As we see in the latest Endgame trailer, the Mad Titan has the blade when he's confronted by Iron Man, Captain America and Thor. The reason for the blade may be relatively straightforward, to deal with "minor" obstacles that don't require the cosmic power of an Infinity Stone. But if that were the case, why didn't he use use the weapon in Infinity War? He's already defeated the Avengers and their allies once. Therefore, it stands to reason something significant has changed.
It's possible Thanos is using the new weapon because he no longer has access to the Infinity Stones. The first Endgame trailer seemed to reveal a mangled Infinity Gauntlet, which makes sense, considering the damage done to it by the snap. Granted, the Mad Titan did teleport out of Wakanda at the end of Infinity War, and the first clip from Endgame indicates he's used the Gauntlet at least once since then. However, there's a chance that at least some of the Infinity Stones have been damaged.
Bolstering the idea that Thanos can no longer access the full powers of the Infinity Stones is his apparent means of teleportation in the latest trailer. This being Marvel Studios, we can't dismiss the possibility that footage has been altered. However, if it is legitimate, it brings major implications. It would seem to be the same technology used by the Black Order in Infinity War and, as such suggests, Thanos isn't using the Space Stone to crisscross the galaxy. He may be physically vulnerable, which could lead to him requiring another weapon to wield against Earth's Mightiest Heroes.
In Infinity War, Thanos defeated the Hulk and choked Loki to death without the use of a weapon, but that was the Mad Titan arguably in his prime. We don't know what effect the snap had on him, although the glimpses we've gotten of him in Endgame hint that damage has been done. That doesn't mean he's weak, necessarily, but perhaps weaker than before.
The remaining Avengers have also had time to plan for their offensive, and recruit the cosmic equalizer Captain Marvel; this isn't the same as in Infinity War, when they were caught off-guard. Thanos may actually fear them. Heck, Thor nearly killed him during the Battle of Wakanda, so Thanos has reason to arm himself for the rematch.
With the Black Order gone and the Outriders hardly on the Avengers' level, it's understandable that Thanos would want to have a new weapon. He no doubt knows the Avengers won't simply give up. Desperate times call for desperate measures, and this weapon might be his last line of defense.
Directed by Anthony and Joe Russo, Avengers: Endgame stars Robert Downey Jr., Chris Evans, Mark Ruffalo, Chris Hemsworth, Scarlett Johansson, Jeremy Renner, Don Cheadle, Paul Rudd, Brie Larson, Karen Gillan, Danai Gurira, Benedict Wong, Jon Favreau and Bradley Cooper, with Gwyneth Paltrow and Josh Brolin. The film arrives April 26.