X-Men: Endangered Species One-Shot

Marvel's 2007 one-shot X-Men: Endangered Species serves as a pivotal bridge between major storylines, with writer Mike Carey and artist Scot Eaton charting the Beast's desperate, morally complex quest to reverse the Decimation—the event that left most mutants powerless. This single issue matters as a focused, character-driven meditation on scientific ethics and the lengths one hero will go to save his kind, setting the stage for the fallout to come.