In this post I noted how one issue of Timely's KRAZY KOMICS took a subordinate character, The Creeper, from a strip called "The Vagabond" and made him a co-star of a strip about a rabbit-detective named Homer. Only this first "teamup" counts as a crossover of these two characters. A little later The Creeper was joined in his nutty nefarious activities by his lookalike son "Crawler," while Homer and his allies kept chasing the two of them down. In KK #9-10 the antagonists visited "Fairy Land" (which might as well be the story's title) and met...
RED RIDING HOOD and her WOLF KING MIDAS and THE OLD WOMAN WHO LIVED IN A SHOE.
THE THREE BEARS and the GIANT from "Jack and the Beanstalk"
SIMPLE SIMON, WILLIAM TELL, and three characters from the "Hey Diddle Diddle" rhyme.
KRAZY KOMICS #7-9 also played host to a three-part story teaming up a new character, a beneficent fairy named "Inky the Imp," with a "Fractured Fairy Tales" version of the Pied Piper of Hamelin and his mice (who are the Piper's allies this time).
In KK #11, though the "heroes" and their "villains" aren't in Fairy Land anymore, they still meet a "King Arthur" who looks more like Old King Cole.
KK 12 then asserts that all of the Krazy Komics characters inhabit their own world, and The Creeper magicks some of them into the "real world." They try to protest their treatment in the comics to the creators of Timely Comics (all of whom are caricatures of the real raconteurs). I recognize only Ziggy Pig, Silly Seal and Super Baby, but the main characters are still Creeper, his son Crawler, and the rabbit Homer.