Though the Quality character Kid Eternity conjured up dozens of mythical and historical characters in his crime-fighting career, I've just written a rationale here as to why the majority of them are not crossovers, except for those that are nominatively fictional...
Like Blackhawk...
And Sherlock Holmes.
In addition, the Kid hadn't even around for four adventures before someone-- possibly theoretical writer Otto Binder-- decided to use the hero's adventures in HIT COMICS to spin off a pair of comical villains, who made two appearances as adversaries to the Kid, and in HIT #28 began their own long-running backup series. Once they were there, I doubt that they ever again darkened Kid Eternity's door until the 1970s, when all three characters appeared in one of Nelson Bridwell's "Marvel Family" stories.
The title of the strip was "Her Highness," after the otherwise unnamed gnomish female who was theoretically the brains of the two-girl outfit. Yet the svelte stunner named Silk functioned as both the "straight woman" of the strip and as eye-candy for male readers who found the old broad less than engaging. I haven't read all of their capers but their usual schtick was that the two females tried to initiate some grand swindling scheme and accidentally ended up busting up some other criminal's operation, and thus providing entirely unintentional assistance to the forces of law and order.
