Nyxlygsptlnz was a 5th Dimensional princess, the daughter of the King of Zrfff. She fell in love with Mxyzptlk, much to the chagrin of Vyndktvx, who was driven insane with jealousy. To hide from him, she was forced to hide on Earth, where she was born as a human baby.
She was the land lady of Clark Kent's first appartment in Metropolis, where he knew her as Ms. Nyxly.
In previous continuities, she was known simply as Gsptlsnz, or Gzptlsnz, and is typically Mxyztplk's girlfriend or a love interest thereof.