Clue Comics was a rather odd comic series. While its cousin, Air Fighters, had a clearly distinguished internal theme (mostly military aviation), Clue Comics' internal theme, crime stories, were flouted rather egregiously by the lead feature for most of its run, Boy King and his Giant.
It was also crippled by, let's be honest, the fact that more than one of its staff members seemed to be "doing dope," as a background character in one of the features once speculated in response to an oddly behaving individual. Nowhere was this more apparent than in the awful "Nightmare and Sleepy" feature, which was actually at its best in one of the very last issues of Clue Comics, volume 2 issue 1.
That's not to say it was good.
They also kind of forgot the "and Sleepy" part, which doesn't really make a difference.
It's interesting to note that here, Nightmare got an alternate origin-rather than being a wandering dude who randomly fought weird crime in bizarre locales (seriously, it was a hecka weird comic), he emerged from the smoke of a private eye's homemade cigars and beat up crooks who were threatening the man.