"Chutes and Ladders"
Before I begin, I have to make a comment that while I've had some fun poking holes in some of Chris Claremont's excesses and strange choices of plotting and pacing, he has written some incredibly good and important stories. And Uncanny X-Men #160, which introduces the character of Belasco and the dimension of Limbo, is one of those. The story begins (as so many X-Men stories do) with the X-Men in training while some distant figure watches them. When Colossus little sister Majik wanders off into the ancient temple where the X-Men are currently making their base, they disappear into teleportation discs, and find themselves in a mirror universe where nothing makes sense. And they find that they might have been here before, or might still be here: they encounter a Nightcrawler who has turned bestial and attempts to molest Kitty Pryde, they find an eviscerated Colossus hanging on the wall, and they see a shadowy figure who might be helping them...or hurting them. In 18 pages, not even the entire story, the entire X-Men mythos is upended and we are shown a world where they can't save the situation with a fastball special or a lightning strike. The story managers to create an atmosphere that the physical and psychological danger is for real. At the end of the story, Colossus younger sister, Illyana Rasputin, returns to earth six years older, with the explanation of what she was doing in the intervening years not explained until a year later, in the Majik limited series.
That story was so important because it went beyond the X-Men's normal melodramatic family dynamic to show it as an actual abusive family dynamic, with Belasco being not only a demon lord, but also a master manipulator: in some ways, perhaps, a dark shadow of Professor X, whose aloof manner and mental powers over a group of younger people could certainly be seen in a less favorable light. In the Majik limited series, we are given a description of how claustrophobic and corrupting it felt to be under the total control of a master manipulator. And in this story, we get a hint of that.
But here is where I have to be a little critical. When Alan Moore was given the Charlton Comics characters to write about, he produced Watchmen, one of the most significant comic stories ever. But, the editors at DC made him change some details, using variants of those characters, because they said they would need to use those characters in the future. And that is almost what happens here: Chris Claremont almost creates alternative versions of the X-Men to use in a much darker, self-contained story...but then, at the end, the entire thing was treated almost as a dream. And at the end of this story, we are going to return to a larger arc with a much different tone: after all, we still have two space princesses fighting over a throne in an ongoing space opera. So I really was impressed by how much of a different tone this story created---but then remembered that it would be forgotten by next issue, as the story rushes on.