Captain Marvel has proven to be one of the most powerful heroes in the Marvel Cinematic Universe, even being able to go toe-to-toe with arguably the deadliest villain in the universe, Thanos. The two came to blows during the climax of Avengers: Endgame as Carol tried to secure the Infinity Gauntlet. It's in that moment we see Thanos headbutt Carol, trying to overpower her, but Carol barely responds.
During the final battle, was Captain Marvel getting an unexpected power boost thanks to the other Infinity Stones - and did Thanos breaking it allow him to blast her?
Thanos vs. Captain Marvel
During the climactic final battle between the assembled Avengers and the armies of Thanos, the heroes seem initially overwhelmed by the superior firepower of Thanos and his ships. However, Captain Marvel is able to descend onto the battle after traveling across the cosmos. It doesn't take her long to prove to be the most capable and powerful hero among the Avengers, quickly bringing down Thanos' flagship and proving crucial to trying to procure the Infinity Gauntlet. Eventually, Captain Marvel ends up being one of the only heroes who has the strength to confront Thanos head-on on her own. It's quickly apparent that she's more than powerful enough to stand up to Thanos.
Her speed, flight, and energy blasts give her a way to attack him without getting too close. She's even strong enough to force his hand open, keeping him from activating another snap. Thanos tries to incapacitate her with a headbutt, but Captain Marvel doesn't even flinch. Just as she's overpowering Thanos, however, he pulls the Power Stone from the Gauntlet and, coupled with his natural strength, manages to punch the hero briefly away. But, how is Captain Marvel so powerful--and how did Thanos get enough power to slow her down?
The Power Boost
As revealed in Captain Marvel, Carol Danvers was just an ordinary human being until she was exposed to the energies of the Space Stone - one of the six ancient and powerful Infinity Stones. The Stone was being used us an energy source by Miranda Lawson aka Mar-Vell, a scientist who was trying to figure out how to develop faster-than-light engines. But, she was attacked and killed during a test flight. Her co-pilot, Carol, destroyed the engine but was caught in the ensuing explosion. This exposed Carol to the energies of the Infinity Stone and changed her body, granting her extreme power the likes of which can't be compared to.
She's possibly the single most powerful hero in the MCU, with the Infinity Stone literally empowering her and imbuing her with all that power. So, how was Thanos was able to even slow her down? Thanos might have gotten his opening thanks to Captain Marvel accidentally getting a power boost. Being full of energy from the Infinity Stone is the source of Captain Marvel's powers. However, each of the Infinity Stones are shown being even more powerful when used in concert. Carol possibly received received a power boost from being so close to the other Infinity Stones, creating a circuit that made her more capable in a fight. This even explains why during the fight, the two begin more as equals until Captain Marvel starts to overpower him.
If that was the case, then Thanos breaking the Infinity Stone circuit may have been even more devastating than he realized. On top of gaining the natural boost that comes with utilizing the Power Stone (so long as you're powerful enough to withstand those energies), Thanos might have inadvertently broke the energy chain and cut off Carol's ability to be empowered by all the Stones being in concert. While it certainly doesn't put Captain Marvel down for the count, it does explain how the single hit from the Power Stone was able to surprise her so much and send her flying. Captain Marvel may not have even realized that the power boost was happening, and so her surprise could have been a mix of the power drop as well as Thanos getting in a sneaky hit.
Regardless, Captain Marvel did her job in the end -- she was able to hold Thanos at bay long enough for someone like Iron Man to figure out a full workaround to defeat Thanos. With the Infinity Stones gone, Captain Marvel may now be one of the last few vestiges of that cosmic power in the entire galaxy. While she may not get that kind of power boost again without the stones, it still makes her exceptionally powerful in the grand scheme of things.