The X-Men #9 (1965)

In the X-Men #9 (1965), the world is in danger as Professor X warns Cyclops never to let Lucifer threaten Earth again. The X-Men's leader, Cyclops, teams up with the Professor to pursue Lucifer before he causes any harm. However, their mission gets complicated when the Avengers also join in. The two superhero teams engage in an epic battle, with the Avengers wanting to defeat Lucifer while the X-Men are committed to not hurting him. Professor X uses his extraordinary telepathy to put Lucifer to sleep and ultimately disables the bomb. With collaborations from both teams, they are able to neutralize any danger presented by the villain. The X-Men #9 marks the first-ever team-up between The Avengers and the X-Men, making it a significant read for any comic book enthusiast.