Source: Action Comics #579 (1986) Type: The real deal + magic potion (since retconned)
It's all Jimmy's fault. He breaks a magic shield from Gaul circa 50 B.C. and it transports him - and an amnesiac Superman - through time to an Asterix homage/crossover. It's also a tribute to the kind of time travel stories that were frequently told in Jimmy's own book through the Silver Age; he's definitely the hero, and even takes Asterix's place in the story, drinking magic potion and fighting at faux-Obelix's side. It's one of my favorite "lame duck Superman era" stories, and I've invoked it several times. So the same way Jimmy travels back in time to Ancient Gaul, this link will Delorean you back to April 19th, 2008 when I covered the story in the most detail.