It's an homage. Both covers are done by Romita. The #190 X-Men has Kulan Gath exacting his revenge on Spider-Man for what he and Red Sonja did to him in Marvel Team-Up #79. Uses a spell to turn Manhattan into a barbarian world where the X-Men and Avengers have no memory of the present. He leaves Spider-Man's memory intact as punishment, and has him hunted by his mindless slaves. I think the story arc starts on issue #189 and ends in #191. Many heroes die, including Spider-Man, but Dr. Strange uses a spell to bring reality back in time to the moment before Kulan Gath appears. At the time Dr. Strange doesn't know it, but what he's done brings Nimrod to their timeline. So I think Nimrod's first appearance is X-Men #191. My question is why Red Sonja doesn't have an appearance in any of this? Oh, I should mention that in the Dynamite Red Sonja series Kulan Gath makes his first appearance in issue #12.