Inferno
Demons from Limbo try to take over the world. They transform New York into a demonic state, the Empire State Building grows, many technical things are possessed and demons rain down from a large teleportational stepping disk over Times Square. Jean Grey and her look-a-like Madelyne Pryor meet for the first time. Magik has to confront her dark side.
- Storm, Wolverine, Havok, Psylocke, Dazzler, Longshot, Rogue, Colossus (X-Men)
- Archangel, Beast, Cyclops, Marvel Girl, Iceman (X-Factor)
- Cannonball, Mirage, Sunspot, Wolfsbane, Magik, Warlock, Gosamyr (New Mutants)
- Skids, Rusty, Boom-Boom, Rictor, Leech, Artie, Wiz Kid (X-Terminators)
- Shadowcat, Meggan, Captain Britain, Nightcrawler, Phoenix III (Excalibur)
- S’ym, N’astirh, Crotus (Limbo demons)
- Goblyn Queeen / Madelyne Pryor
- Baby Christopher
- Mr. Sinister
- Arclight, Harpoon, Sabretooth, Prism, Scalphunter, Malice, Vertigo, Scrambler, Blockbuster, Riptide (Marauders)
The main plot is in New Mutants (1st series) #71-73, X-Factor (1st series) #36-39 and Uncanny X-Men #240-243, but X-Terminators #1-4 and Excalibur #6-7 are also closely connected.
Inferno was a line-wide crossover so the effects were seen in any other Marvel title of the time too. For example the Human Torch could not turn his powers off due to demonic influence and Captain America was seen fighting demons in the pages of the Avengers.
Some of these other issues are : Amazing Spider-Man (1st series) #311-313, Avengers (1st series) #298-300, Cloak and Dagger #4, Damage Control (1st series) #4, Daredevil (1st series) #262-265, Fantastic Four (1st series) #322-323, Power Pack #42-44, Spectacular Spider-Man #146-148 and Web of Spider-Man #47-48
Prologue :Uncanny X-Men #239
01) X-Terminators #1
02) X-Terminators #2
03) X-Terminators #3
04) New Mutants (1st series) #71
05) X-Terminators #4
06) New Mutants (1st series) #72
07) Uncanny X-Men #240
08) Uncanny X-Men #241
09) X-Factor (1st series) #36
10) X-Factor (1st series) #37
11) New Mutants (1st series) #73
12) Uncanny X-Men #242
13) X-Factor (1st series) #38
14) Uncanny X-Men #243
15) X-Factor (1st series) #39
--) Excalibur #6
--) Excalibur #7
For months now Madelyne Pryor had been in secret contact with N’astirh who had awakened her latent powers through his magics. Calling herself the Goblyn Queen she was nearly insane and Mr. Sinister revealing her origin did not help. Maddie was only a clone of Jean Grey, animated by some residue of the Phoenix Force, whose purpose was to conceive the child of Cyclops. With the genes of both Summers and Grey this was to be the ultimate mutant. Boiling mad Maddie gave in to N’astirh’s offers and intended to sacrifice her own child to hurt the two men responsible for her misery : Sinister and 
Cyclops. The baby’s death would have permanently established the link between earth and Limbo. It took the combined might of both X-Men and X-Factor to fight the demons while Jean and Maddie fought each other. In the end the Goblyn Queen killed herself and tried to force Jean into a mental bond to die with her. Jean was saved by the remnants of the Phoenix Force. Left with no other choice Jean had to integrate both the personalities of Phoenix and Maddie into herself to survive.
Both X-teams then battled (and apparently killed) Mr. Sinister, who was discovered to have been manipulating Cyclops’s life since early childhood.
At the same time the New Mutants and the X-Terminators tried to disrupt the large pentagram over Times Square and were unable to help their teammate Magik. Illyana had been tricked by Nastirh into opening the portal and now both he and S’ym tried to turn her into the Darkchylde by daring her to use the soulsword irresponsibly. Magik transformed more and more, she grew fangs, horns, hooves and a large tail, but the sudden arrival of her brother Colossus helped her to focus. Finally Illyana cast all her magical might into one spell and threw the Soul Sword into the large stepping disk portal. All demons were sucked back to Limbo and it seemed as if the teenage Illyana had never existed; in her place was the seven year old child that originally had been kidnapped by Belasco and taken too Limbo so many months ago.
X-Men :
- Longshot felt tainted after he was influenced by the demons during Inferno. He left the team in Uncanny X-Men #248 on a quest to find his inner peace.
- Seeing Sinister die loosened Malice’s hold on Polaris. Lorna regained control and could contact the X-Men for help.
New Mutants :
- Illyana was reduced to childhood and brought back to her parents in russia.
- The New Mutants finally parted with Magneto, the school’s current headmaster, since they witnessed him and the Hellfire Club make a deal with the demons.
- The teenage members of the X-Terminators (Rusty, Skids, Boom-Boom, Rictor) joined the New Mutants.
X-Factor :
- Cyclops was finally reunited with his son.
- Jean had troubles to deal with the added personalitys of Madelyne and Phoenix for quite some time.
- Beast gave Warren the name Archangel during Inferno, thinking this to be more fitting than Dark Angel.
Excalibur :
- With Illyana gone the Soul Sword appeared with Kitty. Since she did not want it the sword was left in a stone before Excalibur’s lighthouse. Years later the sword was given to Amanda Sefton.