Goy is the child of Mal Timmy and Trixie. Unlike other children, Goy has a girl side and a boy side (Both sides are evil, though). That is how Goy got his/her name.
After Timmy fought with Mal Timmy, Mal Timmy went to Dimmsdale Reformatory School. Just six days later, Trixie got busted by her sister, Vanessa, and was sent to Dimmsdale Reformatory School as well. The two met, fell in love, got married and Presto! Trixie gave birth to a son/daughter named Goy! And that is why the three now live happily ever after.