WARNING: The following contains spoilers for Doctor Strange #10 by Mark Waid, Jesus Saiz, Jim Campbell, Kevin Nowlan, Butch Guice, Carlos Lopez, Tom Palmer, Daniel Acuna and VC's Cory Petit.
In the landmark 400th issue of Doctor Strange, Marvel hasn't just made a big change to the mythos of magic on the whole, it's brought a key arc into the comics that proved to be the plot driver of Scott Derrickson's Marvel Cinematic Universe movie starring Benedict Cumberbatch.
In the 2016 mystical battle royale, we saw Kaecilius wage war on Doctor Strange, Mordo and the Ancient One for drawing energy from the Dark Dimension. Over two years later, in the relaunched title under Mark Waid, Issue #10 sees Dormammu and his kind launching a similar attack on Earth because Strange has followed suit with the MCU, going overboard and drawing power from the Dark Dimension with no concern about paying it back.
Just to recap, Tilda Swinton's Ancient One was the one extracting the essence of the Dark Dimension because, as she told Strange before she died, she needed to break the rules for the greater good. Drawing this dimensional energy helped her protect Earth and Kamar-Taj, but it also incurred the wrath of Kaecilius, her former student who thought she was a hypocrite, as well as Dormammu, who didn't appreciate his dimension's energy being depleted.
Issue #10 now dives deeper, as the Sorcerer Supreme finds out the true cost of using magic over the decades -- and that he's racked up a near infinite debt. Strange discovers Marvel's magical accountant, Hothran, was the one who took his powers away in the debut issue of this run simply because Strange wasn't paying back his debtors, and was in fact using up magic more than he was repaying. When he wandered the cosmos and re-learned how to use magic, Strange was actually pulling from unknown alien dimensions, which meant his debt doubled. This threw the entire idea of magic into disarray because these new sources of magic were deadly, ruthless and uncontrollable.
Simply put, these owners don't play nice and the accountant is now trying to balance the books and save magic on the whole. Unfortunately, Strange has pulled carelessly from Dormammu's Dark Dimension -- something he finds out when his inner circle is held as collateral by the accounting agency. Every time he utters "By the Flames of the Faltine" or "Wand of Watomb," he uses a fraction of someone else's power, and it seems Dormammu's Faltine race has finally had it, deciding Strange needs to be taught a lesson in economics. They've come to collect by razing the Earth, which Dormammu is all too keen to enjoy as mystical repo man.
As the Faltine engulf the planet in flames, Strange's arrogance once more proves to be his biggest downfall, as he is finally understanding -- albeit too little, too late -- the cost of magic is steeper than he once thought. It will be interesting to see how he plans on paying back his debt, but hints have been dropped that he'll be playing mind games similar to how he outsmarted Dormammu in the MCU via a time loop.
As it stands, he needs to use his brain more than his hands because casting spells is a double-edged sword, as it's what put Earth in peril at this very moment. Strange could choose to tap into greater reservoirs to defeat this threat, but again, it'd simply mean he'll be bringing more collectors home in the future, potentially ticked off that he's abused this magical privileges. Only time will tell how he solves this, but seeing as the Ancient One has also been deprived of his magic by the accountant, Strange is running short of options and allies, and if he does decide to take another loan, he could further doom everything he holds dear on a much more permanent basis.