Before the current Krakoan Age of the this version of Magneto's Brotherhood was only seen in action once and never again.
Magneto is perhaps best known as a villain, although he has actually spent more time as a hero in his publishing history, and is often associated with two major groups of villains, the Brotherhood of Mutants and the Acolytes. Since the early 2010s, Magneto has been almost exclusively a good guy or anti-hero, but after dealing with a truly horrendous attack during the course of X-Men Blue Magneto had a mental breakdown, and afterward decided to reform his Brotherhood with a new roster.
X-Men Blue - written by Cullen Bunn with art by Jorge Molina and Matteo Buffagni - followed the time-displaced original X-Men forming a new team trying to reestablish the X-Men as a force for good in the public. Working with Magneto in secret, who everyone thought was dead, X-Men Blue did amazing work to win public favor. Magneto reformed his Brotherhood of Mutants will an all-new group of characters: Toad, Marrow, Elixir, Exodus, Unuscione, and the human-cyborg Briar Raleigh.
This group of mutants is truly unique, especially with the reunion of Magneto and Exodus, who used to believe that Magneto was akin to a mutant messiah, and also the addition of Elixir, an old student of Magneto's who has an interesting history of doing whatever is needed to save mutantkind. Sadly though this new Brotherhood is only seen once more, on a screen in X-Men Blue #36, the final issue of the series, prompting the X-Men Blue to go and stop their attack on an anti-mutant rally before they time travel back home. After the ending of X-Men Blue the X-Men universe pivoted into X-Men Disassembled, then Age of X-Man, before relaunching in the Krakoan Era with House of X/Powers of X, meaning Magneto's awesome new Brotherhood team never got to truly have their spotlight!
Thankfully Magneto is now forming a new Brotherhood of Mutants, working with the Regent of Arakko Storm and the New Mutant Sunspot to protect the mutant planet Arakko from threats both internal and external! Any fans of Magneto should definitely check out his appearances in X-Men Blue and make sure to pick up the ongoing X-Men Red to see what's next for his new Brotherhood.
