Warning: Contains spoilers for Iron Man #17
Besides Kryptonite, magic is the Man of Steel's biggest weakness, and Marvel Comics is using the same concept to take down a character that has become so powerful that Superman won't even stand a chance against him: Iron Man.
In recent Iron Man issues, Tony Stark embarked on a quest to stop Korvac, one of the Avengers' earliest foes. Obsessed with recovering the Power Cosmic he once possessed, an almost unlimited source of energy that is usually wielded by Galactus, Korvac successfully infiltrated the Devourer of Worlds' ship, with Iron Man and his team hot on his heels. A confrontation ensued, and both Korvac and Iron Man accessed the source of the Power Cosmic, becoming godlike beings. In the reality-shattering fight that ensued, Tony Stark emerged victorious, becoming the Iron God and returned to Earth to put his immense new power to use for a higher purpose. Motivated by the belief that he was never able to make a true difference for the world despite his great intellect, Tony Stark decided that the best use of his godlike powers was to make every citizen of New York as smart as he is, creating a whole city of super-geniuses.
Despite Tony's good intentions, his judgment is being clouded by a power that was never meant for a mortal. In Iron Man #17 (by Christopher Cantwell and Ibraim Roberson) Patsy Walker, aka Hellcat, fearful of the consequences of the Iron God's actions, enlisted the help of one person who was unaffected by Tony's gift and can thus attack him from an unexpected point of view: Doctor Victor Von Doom. All the heroes in New York now have genius-level intellects but, in truth, they simply possess a copy of Tony's abilities, meaning he could predict anything they come up with. Doom's "unique and unmatched genius," instead, came up with a plan to strip the Iron God of his cosmic powers, with the help of the Silver Surfer, who has been wielding the Power Cosmic for his entire long life. The big obstacle, however, is that Tony made everyone in the city agree with what he is doing because he was tired of hearing criticism. How were Patsy and her team able to avoid that? Simple, with a spell. Doom is not only a genius scientist, but he is also a master of the mystic arts, and this skill has proven once again to be his strongest weapon.
In DC Comics, magic is Superman's major weakness besides Kryptonite, as established in 1964’s Superman #171. Rather than actually being weak to magic, Clark is simply not impervious to it as he is to the majority of other forms of energy or harm. This plot device was used by writers to put the brakes on Superman's powers for the sake of storytelling (villains needed to be a believable threat), especially in Justice League stories. It seems that the same concept is being used now to contain the Iron God: Tony is almost omnipotent, as the Power Cosmic can make almost any wish come true. There is no way that he could be opposed, except by the other Marvel cosmic beings, who however have ruled to not intervene because apparently this was Tony's destiny. Doctor Doom's magic, then, could be the one obstacle the Iron God did not expect, but it proved insufficient to stop his cosmic might. Doom, Silver Surfer, and a group of Tony's closest friends were all killed by the Iron God in a moment of rage, with Hellcat the only one left standing at the end.
Because magic is by definition versatile and unpredictable, it's often used in superhero comics as a storytelling device to balance the odds. Just like with Superman, magic could be the only thing able to stop the Iron God, and to help Tony Stark from losing his humanity forever.