10. Mr. Mxyztplk appeared as a means to lighten the stories during the war
In 1944 a new character appeared in Superman’s universe, first in the daily comic strips, and later in Action Comics. Depicted as an imp, bald, in a purple costume with a green bow tie, he is free from the restraints imposed by the laws of physics. Sometimes called Mxy, he can only be tricked into returning to his home world, said to be in the fifth dimension, by getting him to either spell or pronounce his mouthful of a name backward. Mxy learned of Superman’s world via a book, and traveled to it intent on using his proclivity for practical jokes and seemingly unrestrained powers to take over the world. After encountering Superman, his motives changed in the 1940s, and he appeared desirous of simply tormenting Superman by creating endless emergencies to which the Man of Steel must respond.
If tricked into saying his name he finds himself instantly transported home, for a minimum of 90 days, giving Superman a badly needed period of rest. Mxy was initially more of a lighthearted villain, pulling pranks which embarrassed, rather than endangered his victims. In later iterations of the character he became more dangerous and a formidable enemy. At one point, in a later iteration of Mxy, Superman travels to the fifth dimension to turn the tables on his pesky foe. Mxy caused another change in Superman regarding his powers. In the 1950s it is explained that Superman is susceptible to magic, and since Mxy’s acts seem as if they are created by magic (the kind of magic which would occur if the laws of physics are suspended) he can easily defeat Superman.