Content warning: This story contains discussion of the Holocaust
Nightcrawler's teleportation ability has always made him stand out among the X-Men characters. In a series where telepathy, super strength, healing factors, and energy beams are frequently reused and repackaged for different heroes, Nightcrawler remains one of the very few teleporters in the bunch. In a 2005 comic by filmmaker Kevin Smith, it’s revealed why Nightcrawler’s powers are so rare among mutants, and the reason is horrifying.
Spider-Man/Black Cat: The Evil That Men Do — written by Smith with art by Terry Dodson — follows its titular heroes as they investigate a drug dealer who teleports heroin into the user’s veins. This is a service for high-profile clientele who don’t want visible evidence of their usage on their body, such as models and athletes. To get a better understanding of teleporters, Spider-Man and Daredevil summon Nightcrawler for a rooftop chat on the subject in the series' fifth issue. Nightcrawler delivers a brief lesson to the pair that connects teleporting mutants to one of the worst events in real-world history.
Nightcrawler explains that During World War II the Nazis notoriously experimented on human test subjects, one of the many incalculable horrors of the Holocaust. In the Marvel Universe these experiments extended to mutants, expanding the allegory of mutants as oppressed people. Nightcrawler describes an event called the Lebengebrochennacht, or the "Night of Broken Lives" where mutants under Nazi occupation were rounded up and experimented on by real-life monster and SS officer Josef Mengle, also known as he “Angel of Death.” Teleporters were specifically targeted in hopes of replicating their abilities on the battlefield. While there were some successful subjects, mainly children (called “Weing Taktreisenders," or "Little Time Travelers” by the Nazis), among the countless who did not survive, Adolph Hitler’s fear of their potential retaliation led to most of the others being executed as well. Only a few test subjects were fortunate enough to survive long enough for the Allies to liberate the camp.
As a result of these inhuman experiments, not only were the lives of many teleporting mutants lost, the human-hybrid test subjects' teleportation powers genetically deteriorated over time. As generations passed these abilities on, they weakened, or remained dormant. Nightcrawler states that he’s only ever met two other teleporters with his level of ability in his entire life. It’s possible there was once a higher concentration of teleporters in Eastern Europe, considering where these experiments took place, their impact on teleporters' population numbers, and the fact that Nightcrawler himself is German.
It’s well established in X-Men lore that mutants were targeted in the Holocaust. Characters like Magneto, Mr. Sinister, Cruel, and Namor have all been connected to that unspeakable event in some way. While this could be viewed as trivializing an intensely serious matter, it can also be viewed as the series committing to taking its own professed politics seriously. The X-Men are an opportunity for readers to identify with heroes who face oppression and persecution. If you want to have an honest conversation about hate, you have to acknowledge its history. Nightcrawler's revelation about why there are so few teleporters among the X-Men is a classic example of Marvel's "world outside your window" style of storytelling.