Pink X is a villainess who represents the female version of Red X. She claimed to be Red X's daughter (though Red X has no child, and appears too young anyway), and was actually Kitten in disguise. She appeared only in the story "Bad Girls", Issue #41 of Teen Titans Go!.
While Robin was fighting against her, she said: "Finally I got to dance with the Boy Wonder", and commented on his appearance as "cute". Robin can tell right away that "Pink X" likes him. Robin then understood Pink X to be none other than Kitten in disguise.
Pink X's mask was also seen in Kitten's bedroom as a cameo.