Mr. Mxyztplk of Earth-2
From superman.nu: Supermanica
Mr. Mxyztplk of Earth-2
From September-October 1944, the date of his textual debut (S No. 30/3: "The Mysterious Mr. Mxyztplk!"), through March 1955, Mr. Mxyzptlk's name is consistently rendered as Mr. Mxyztplk, i.e, with the letters 'p' and 't' transposed (S No. 96/2: "Mr. Mxyztlpk--Mayor of Metropolis!"; and others). In September 1955, however, both spellings are employed (Act No. 208: "The Magic of Mr. Mxyztplk"), and, from August 1959 onward, the new spelling—Mxyzptlk—is used exclusively (S No. 131/1: "The Menace of Mr. Mzyzptlk!"; and others). (TGSB)The original spelling and appearance of this character are later attributed to the Earth-2 version of the character (See Superman of Earth-2).
See also: Mr. Mxyzptlk