User blog comment:Wachowman/Who Will Survive SSB5?/@comment-24529455-20141018233754/@comment-25161957-20141021062335

We can prove this by looking at Jigglypuff's palette swaps. Let's see here.

Well there's Serena's hat (the female player. Note Calem can't wear that hat.), the Fairy Tale Girl's ribbon (a female NPC), Phoebe's flowers (a female member of the elite four), Nurse Joy's hat (a female NPC), Leaf's hat (another female player. Note that Red does not ever wear this hat ever.). The only exception to this rule is Yellow's hat (a female character from the manga, but during her character arc she was hinted to be "male"). So unless that one hat debunks Jigglypuff's gender, Jigglypuff is definitely female.