I should have known by the ending of the first Xenmu story back in July 1960 that he would return. In Journey into Mystery #66 (Dec 1960), he does this very thing – being the only “giant Marvel monster” to appear in the last couple months. Production trouble at Atlas/Marvel? Or maybe a re-thinking of their strategy? (after all they would soon re-pivot to be a superhero-first comic book company in about a year)
Anyway, this time around, the Hulk manages to steer in asteroid into his spaceship-prison and bump him into landing on Earth. Mentally drained, he imprisons a small town to build him a reflector that can super-charge him again to mass-hypnotize the planet. Good ol’ Joe Harper catches wind of the plan and goes to face off against the Hulk again. He brings a mirror and when the Hulk tries to hypnotize him, he ends up hypnotizing himself out of existence.
In the midst of all the world-building that DC is doing, it seems that Atlas continues to try to forge its own path. Even an attempt to bring back a recurring character in one of its anthologies is put to a quick end, with Joe Harper not even being named in this story :-/