Literally Non-Binary Petz
There have been numerous instances of petz that were thought to be "female" having babies with other "female" Petz. Upon examination it was found these petz have special genders. Normally Petz have either 00 (male) or 01 (female) gender. But for some reason sometimes another hex number ends up there. I first encountered it with my cat "honey bunch", turned out their gender was "FF"
"Non-binary" Petz can mate with male or female petz. They will show as "female" in game. The catch is if you want to mate them with other "female" Petz you can't just use Petz A, they'll need to fall in love the old fashioned way.
You can have any hexidecimal gender you want as long as you rebalance the checksum using math or PetzByte.
If you aren't hex saavy, here "nonby", a little fun cat you can download. Their gender is FF. As they grow they'll look pretty different and they also have a randomized personality and genetics for more fun!