Reddit reviews X-Men: Vignettes, Vol. 1

Hmm, this is kind of a toughie with such limited info to go on. There's been any number of short story anthologies featuring the X-Men. By "a book" can I assume you mean a trade paperback? Could it be this one? It collects various shorts from the second volume of X-Men Unlimited. There's also Manifest Destiny, as well as two volumes of Vignettes, though those are older stories that wouldn't be as overtly dark as you describe. Do any of these sound familiar?

Oops my bad [Vignettes] (https://www.amazon.com/X-Men-Vignettes-Vol-Chris-Claremont/dp/0785108122/ref=sr_1_1?ie=UTF8&qid=1512003346&sr=8-1&keywords=x-men+vignettes) is actually really cheap on Amazon! It's only got a couple Nightcrawler stories but they're good, and the rest is good too.

Nightcrawler is tougher, as he doesn't have a lot of stories where he is the spotlight. The few good Nightcrawler stories aren't well collected, but here's what I'd recommend for good, classic Nightcrawler issues:

X-Men Vignettes, Uncanny X-Men Annual #4, and Excalibur.