The following contains spoilers for Immortal X-Men #3, now on sale from Marvel Comics
The X-Men have found themselves increasingly facing plenty of horrifying possible futures, giving their current tumultuous period all sorts of dangerous endings. This has only been exasperated by the fact that the X-Men finally have precogs after Krakoa briefly outlawed them -- opening the door for lots of other grim timelines to unfold.
Immortal X-Men #3 (by Kieron Gillen, Lucas Weneck, Dijjo Lima, and VC's Clayton Cowles) introduces plenty of dark possible futures that could await the X-Men. It also sets the stage for which enemy might be the true villain of the X-Men's current era.
Immortal X-Men #3 focuses heavily on Destiny. The long-dead mutant prophet has firmly re-established herself as a vital piece of Krakoa since her restoration in Inferno, allowing her to help guide mutants down a positive path going forward. But as a result of the current era's numerous conflicts and problems, she finds herself spending most of the issue dealing with painful visions of the possible futures awaiting the X-Men and their allies. For Destiny personally, the greatest problem is that her lover, Mystique, isn't in a single one of these timelines -- suggesting there is some dark, permanent fate awaiting the shape-shifting mutant in the near future. While she does have glimpses of upcoming confirmed conflicts like Judgement Day, her other visions offer possible darker paths for the mutants in the coming years.
Two of her visions showcase timelines where Krakoa falls as a nation to war. In one of them, the island is seen burning from afar. It's not entirely clear who committed this act, but the island nation seems unprotected -- suggesting these might be worlds where Orchis successfully wipes out the mutants. In another, the X-Men have been betrayed by one of their allies, Magik, a leader amongst the New Mutants and a War Captain of Krakoa. Notably, though, she appears in this vision in her corrupted DarkChylde form, suggesting her current trip to Limbo might transform her back to her worst self. In another future, Krakoa is put into danger by the looming threat of the Dark Phoenix, seemingly returned to Jean Grey, or someone like her, such as Madelyn Pryor.
Quietly the most frightening timeline seen by Destiny is one where the X-Men and their mutant allies ended up under the sway of Mister Sinister -- with new versions of Cyclops, Wolverine, Jean Grey and Emma Frost standing at his side as he sits in a crimson diamond throne. This suggests in at least one possible timeline, Sinister fully turns against the mutants and even wins -- either corrupting them or cloning them to serve him. Sinister is also the villain in another possible future, however, in this one he rebels against the mutants but is forced to leave.
Along with Destiny's visions, there is also a chart of the evolving timeline featured in the issue -- hinting at many more futures that end with Orchis and Nimrod victorious. The timeline that carries the longest lifespan seems to be the future that the X-Men are currently heading towards, as one of the events is listed as AvX VI -- suggesting another battle between the Avengers and X-Men. This possibly fated battle could also have something to do with the upcoming Judgement Day event.
This timeline still has possible dour endings for the mutants at the hands of Orchis, but it also presents two happier endings -- one of "Unity" and one of "Expanse" for the universe. The latter is seen in full, showcasing a timeline where mutants have created a theological empire under the guidance of Exodus. The omega-level mutant is now a god-like figure, seemingly imbued with the Phoenix Force and still hunting Mister Sinister. This helped Destiny discover that Sinister has cloned Moira MacTaggert, meaning the ending of each possible future was created by the death of that timeline's Sinister, resetting events back to Krakoa and allowing Sinister to try again. All of these possible timelines present uniquely dark paths for the X-Men and all seem to suggest that Mister Sinister above anyone else is the true ultimate enemy of the mutant nation, with his efforts to upend and corrupt their mission potentially spiraling until the entire universe is under his sway.