The X-Men are probably the most fruitful team in comic history. There have been no other superhero or supervillain teams with as many spin-off groups as the X-Men have had. From training teams for teen mutants to government sponsored teams to black op groups, the X-Men have all kinds of spin-off teams. The Krakoa Era has seen many of them show up again, working for the government of the mutant nation of Krakoa.
Source：https://www.cbr.com/madelyne-pryor-dark-xmen-members-trivia/
