Largely absent from the Warren/Vanisher plot, Nightcrawler is alluded to be of a differing opinion on how to proceed from Warren. By stepping back, Kurt is basically ceding leadership of the squad to Warren, a reversal from how the team was generally portrayed from issue 395. Part of this is the split on Warren’s plan; mostly, though, it has to do with the confrontation with Church of Humanity, its Supreme Pontiff, and the way that the group smashes up against Nightcrawler’s Catholicism. In issue 400, something happened with the Supreme Pontiff that Kurt doesn’t recall and he’s been increasingly erratic since then, struggling with a ‘crisis of faith,’ as he puts it to Warren in issue 407. In issue 408, he discovered that humans were using the Vanisher’s drug, one that gives humans a temporary mutation, often killing them in the process, in the basement of a Catholic church. Here, he confronts the cardinal of that parish, only to find him in the middle of injecting himself with the drug.
The ensuing mutation and battle is a bit heavyhanded with the cardinal screaming “BEGONE, DEMON!” as he transforms into a hulking form resembling that of the Thing, except with the black of the cracks and yellow/orange/brown of the stone reversed, and glowing red eyes. As Nightcrawler tries to subdue him, he yells “AT LAST I AM CLOSER TO GOD...!” to further demonstrate the subtlety of the scene. Three members of the Church of Humanity then teleport into the church, kill the cardinal for debasing himself and God, and, then, refrain from attacking Nightcrawler despite him being a mutant because “THE SUPREME PONTIFF HAS PLANS FOR THIS ONE,” teleporting away before Nightcrawler can stop them – which is, in and of itself, a lovely reversal to add an extra level of frustration.
In a final issue of a run, it’s a bit peculiar to include a scene like this. There is no point to Casey trying to further this subplot that he won’t resolve, except acting under the principle of the world he’s writing. This is the other side of the “interpersonal soap opera” of superhero comicbooks, where he could rush a conclusion, temporary or permanent, to this subplot... but, that’s not how things are done. Pick up the baton from the previous writer, pass it to the next... that’s the spirit of the work-for-hire writer in a shared universe. Even more than the Warren/‘mutant businessman’ plot, this one feels particularly unresolved. That story does end, to a degree, by Warren buying out the Vanisher’s men and putting a stop to the flow of drugs. Not every future threat can be solved by simply paying a bunch of money to some criminals, so this could be treated as a one-off resolution without too much cognitive dissonance. The Nightcrawler story, on the other hand...
If I recall, it would make up a decent chunk of Chuck Austen’s infamous run that followed Casey’s. In my head canon, it all ends here and how it plays out is unknown. I’m not sure if Casey even knows what happened next – or cared. But, what this shows is his dedication to the tradition of the form and the X-Men in particular. What’s an X-Men comic without a dangling mystery left by one writer for another to resolve? When Casey was on Cable, he began trying to resolve a previous mystery by bringing back The Twelve and, then, when he left the title in solidarity with Ladrönn, Alan Davis wound up finishing that story in the two main X-Men titles... and one of those plot points, Cyclops’s possession by Apocalypse, would linger enough to play a role in Casey’s first issue of Uncanny X-Men. There’s something fundamental about Casey’s love and respect for superhero comicbooks and the unwritten code about how you do them...
For all that he tries to push the boundaries, particularly at this point in his career, this is still a writer who grew up loving comicbooks. His Uncanny X-Men run is rooted in the tradition of the title, its history, and the shadow of Chris Claremont in particular. He started there and tried to write his way out, eventually hitting that point just in time to be shown the door. The Nightcrawler scenes are less about the character, for our purposes, then what their inclusion says about Casey’s approach to the job. Except, his approach is rooted in doing right by it and the characters... basically, there’s no concern about not finishing the story, it’s about continuing to tell it as long as he’s paid to and remembering that the real author is Marvel Comics. This is the end of Joe Casey’s Uncanny X-Men, not Uncanny X-Men.