>>42653562"It", though I suppose "she" is somewhat acceptable for a creature that is stated to have given birth in the past. Still, it naturally learns Transform so the concept of having a single, static gender might be totally alien to it, making the term "gender unknown" actually a totally valid conclusion to draw.
>>42653957It probably fucked something that wasn't a Pokemon, giving rise to a novel species that resembled the non-Mew parent but was actually a Pokemon.