Warning: contains spoilers for Amazing Spider-Man #51!
Can Doctor Strange undo Spider-Man's worst story, "One More Day?" In 2007, a controversial Spider-Man story saw Peter Parker strike a deal with the Devil - literally. In order to save the life of his beloved Aunt May, he and Mary Jane struck a bargain with Mephisto to have history rewritten. In truth, it was a somewhat clumsy plot device to undo the marriage of Peter and MJ, because Marvel felt it damaged the Spider-Man brand. "One More Day" was controversial at the time, and it's gradually become seen as Spider-Man's worst story.
Marvel has seemed increasingly aware of the story's notoriety, and it's beginning to look as though they're about to undo "One More Day." The demonic Kindred appears to be a pre-OMD Harry Osborn, released from Hell to have his revenge upon Spider-Man. Fortunately, in Amazing Spider-Man #51 the wall-crawler went to Doctor Strange for help - and the Sorcerer Supreme appears to have begun to figure things out. Partway through an enchantment, Strange pauses as he notices something odd about Peter's soul. "Peter," he asks, "have you ever made a kind of... arrangement... in regard to your--" He pauses, shaken by the enormity of what he is considering, and cuts himself off. "No," he concludes. "It's impossible." And he resolves to investigate matters for himself. Whatever is going on, in Doctor Strange's view, is a matter for the Sorcerer Supreme.
All this raises the intriguing question: can Doctor Strange possibly undo "One More Day?" If any sorcerer can, it's Doctor Strange, one of the most powerful mystics the world has ever known. Like any Hell Lord, Mephisto is just short of all-powerful when he's doing battle on his own turf, and he's stalemated a starving Galactus in Hell. But his power is much more limited while on Earth, which is why he tends to strike deals with the unwise and unwary. These agreements essentially create opportunities for him to flex his muscles into our reality.
Dealing with Mephisto is like gambling in a crooked casino; the house will always win. There's almost always a trick in the works, a subtle scheme that will mean Mephisto comes out on top. Indeed, Kindred is most likely Mephisto's endgame, an exquisite way of torturing Peter Parker and all those he loves. But these tricks can actually create opportunities, because they are flaws in the deal that can be exploited once you know Mephisto is involved. If anyone can find a way out of the "One More Day" deal, it's Doctor Strange, and it will be because of his intelligence and experience as well as his magical power.
Even better, nowadays the Sorcerer Supreme is part of a larger group of witches and wizards. Indeed, he's actually headmaster of Strange Academy, Marvel's version of Hogwarts School for Witchcraft and Wizardry, and he can call upon any of his colleagues there. They include Daimon Hellstrom, the Son of Satan himself, and Magik - another Hell Lord, Sorcerer Supreme of the Hell Dimension of Limbo. Spider-Man may end up having good reason to be glad he dropped in on Doctor Strange.