INFERNO! (MARVEL, 1989)
As you can tell by now, some crossovers are wholly original stories, but others are actually based on existing plotlines. “Inferno” is the latter, being made mostly to solve two lingering X-Men related plotlines: one involving Colossus’ sister, Illyana, and another involving Jean Grey’s mysterious lookalike, Madeline Pryor. Sit down and grab a drink, folks, because this is going to be looong:
Illyana became involved with the X-Men when she (along several other friends and relatives of the mutant heroes) was kidnapped by a villain called Arcade. After being rescued by the X-Men, they allowed her to hang around them for a while. Baaaad idea.
In one of their missions, the X-Men went to a mysterious island where a portal to a demonic realm called Limbo existed. (Note: This should not be confused with the Limbo that is the realm of the Avenger’s enemy, Immortus.) The ruler of this realm, the sorcerer Belasco, kidnapped Illyana. The X-Men went to rescue her but, due to the strange way time works in Limbo, they found that she was now a teenager, having lived several years in that world! They brought her back to Earth, where they later found she, too, was a mutant (who had the power to open portals to Limbo, coincidentally enough.) She joined the X-Men’s trainee team, The New Mutants, under the name “Magik.”
But Illyana was keeping a terrible secret: the reason Belasco wanted her, is that he needed an innocent person’s soul in order to form five “bloodstones” from it that he could use to summon his Dark Gods to Earth. The process, however, took years; it also gave her magical powers, including the ability to create a weapon called the “soulsword.” Illyana used it to defeat Belasco before the process was complete (only three bloodstones were made.) Ironically, however, Illyana was now the ruler of limbo, and thus master of all its demons. Another effect was that the more she used her magic powers, the more demonic she became. She developed an evil side called “The Darkchilde” that would occasionally pop up.
As for Madeline, she was a woman who just happened to look exactly like Jean Grey, who had died recently after losing control of her powers (in the classic “Dark Phoenix Saga.”) Scott Summers (Cyclops) found her working for his grandparents in Alaska. Naturally everyone assumed that she was Jean resurrected, but she insisted she wasn’t. After an adventure that seemed to prove her claims, Cyclops and she fell in love, married, and even had a child, a baby named Nathan Christopher Summers. Note: According to the original writer, Chris Claremont, Madeline was indeed meant to be JUST a lookalike, and his way of having Cyclops marry and be happy after he was forced to kill off Jean Grey (that had been Editor-In-Chief Jim Shooter’s idea.) Unfortunately, other people would mess up his plans.
As noted above, somebody else decided to bring back Jean Grey from the dead (supposedly, she never died, The Phoenix turned out to be an impostor who had replaced her) for use in the new X-factor series, which also included Cyclops as a member. So now, Claremont’s plans for Madeline were moot, and it was decided to kill off the character. Inferno was the –rather convoluted- way to do it.
Basically, after Cyclops found out Jean was alive, he went to determine if it was really her, leaving Maddie and the baby alone. Bad idea; they were attacked by the Marauders, who captured the baby, though she got away. When Cyclops came back to look for them, not only he couldn’t find them, but there were no longer any records of Madeline ever having existed! (This was the doing of the Marauders’ master, Mister Sinister.) Baffled, Scott went back to X-Factor. Meanwhile, Madeline contacted the X-Men for help, but they rescued her just in time to be caught in the Fall of the Mutants events. She was one of the persons who agreed to sacrifice their lives to bind The Adversary. This meant that now Scott believed Maddie to be dead, while in reality she was hiding with the X-Men in Australia. From HER point of view, Scott had abandoned her to be with Jean, and she was very bitter.
During a dream she had, the demon called S’ym –Illyana’s second-in-command on Limbo- contacted her, and made her the offer to give her the power to avenge herself on Scott in exchange for her soul. Knowing it was just a dream, she agreed- but apparently, pacts with demons are binding even if they are made in dreams! (Note: later during the crossover, a demon called N’astirh appeared, and seemed to be the one who had actually influenced Madeline. Why the change? Perhaps because S’ym was actually based on Cerebus the Aardvark, a fantasy comic character who did not belong to Marvel; maybe they feared that if they brought too much attention to him, Cerebus’ creator (Dave Sym) would notice and sue them.)
Anyway: After several more convoluted events, Madeline was captured by Sinister, who revealed that she was just a clone of Jean Grey he had created, given false memories and public records. His purpose was to have her procreate a baby with Cyclops, whom he had predicted would have incredible powers that he planned to use to destroy Apocalypse with. Driven mad by all these events, Madeline became the demonic Goblin Queen, and unleashed the forces of Limbo on New York City. Not only did this mean the city was attacked by demons, but even inanimate objects became hellish- toilets would overflow, buses became monsters, etc. Most of the Inferno crossovers featured the heroes of New York City desperately trying to save people amid the chaos. (Hey, where was Dr. Strange in on all this? You know, Earth’s Sorcerer Supreme, who happens to live in New York City? I don’t recall right now, but I’m sure it must’ve been explained. Come to think of it, why didn’t the X-Men ever take Illyana to him for help with her “problem?” Oh, well.)

Madeline tricked the X-Men and X-Factor into fighting each other, and then tried to sacrifice her own baby to make Earth merge with Limbo!! Jean Grey stopped her and after a psychic duel, Madeline committed suicide. S’ym and N’astirh were destroyed, baby Nathan was rescued and Mr. Sinister was apparently killed by Cyclops. Oh, and Illyana, whose portals allowed her to travel in time, finally made the realization that SHE COULD GO BACK IN TIME AND PREVENT HERSELF FROM EVER BECOMING THE DARKCHILDE. File this under “DUH!” It seemed to work, as a seven-year-old Illyana appeared and Limbo’s influence on Manhattan vanished.
Consequences: Illyana was apparently finally saved from her damnation, though strangely, her soulsword still existed; other people would find and use it. (come to think of it, if she had REALLY changed history, none of the Inferno events would have happened, right?) Unfortunately, years later she died from the Legacy Virus, a mutant killing disease. Probably because Marvel didn’t know what to do with her now, and they needed victims for that stupid plotline.
Madeline Pryor was now gone, meaning Scott could go back to Jean without looking like an ass for cheating on his wife. Ironically, decades later Cyclops DID cheat on Jean, who is now dead again, and he has now hooked up with- old X-Men foe The White Queen!? What is this, “Days of Our Lives?”
Oh, btw, Madeline DID return from the dead, too. I think. It’s very convoluted. I’m not going to explain it; go read her Wikipedia article.
And Mr. Sinister also came back, but he’s a villain so that’s to be expected. (They never did explain how, though… maybe he cloned himself?)
And the people of New York convinced themselves that the whole “inferno” thing had been a mass hallucination. Though Spider-Man villain, the Hobgoblin, did become permanently “demonized.”
Baby Nathan would later grow up to become Cable, leader of X-Force.
THIS JUST IN! Believe it not, Marvel is doing a SEQUEL to Inferno! It seems that Belasco, trying to resurrect Illyana, recreated the Darkchilde, but she lacks her innocent soul. She’ll now attack San Francisco (where the X-Men just moved to) in a story to be called “X-Men: Infernus”. Gee, how original. 
My Opinion: Man, was the X-Men series a downer during the 80s or what? This is the third X-Men-related crossover in a row that sucks. Turning Madeline evil just to kill her off was pathetic. But at least they cured Illyana. And some of the crossover stories WERE actually spooky, especially since most people had no idea why Manhattan had suddenly turned into a living nightmare.
My Rating: Below average
Next: 89 was a good year for demons, as the ancient demon Set leads the forces of Atlantis to attack the surface world in Marvel’s “Atlantis Attacks!”