Azurill's Gender SwapPosted November 19, 2017
Pokémon have genders. Three to be precise: Male, Female, and Genderless. Genderless Pokémon tend to be synthetic or non-animal-based in some way (like Magnemite). Genders are used to facilitate Pokémon breeding (that and anything that can breed can breed with Ditto). Some Pokémon have visible cosmetic gender differences (like Pyroar) and the move Attract affects Pokémon of the opposite gender to the user. Those are the general properties of Pokémon gender, but there’s one specific Pokémon called Azurill that could change gender in certain situations.
Some cosmetic gender differences are stupendously difficult to spot
Can’t see the difference above?
That tiny dot. Yes, really.
But we’re not here to talk about Torchic. We’re here to talk about this girl/guy:
Little Azurill, looking a bit distressed
Azurill was introduced in Generation 3 (Ruby & Sapphire). It was one of two new baby Pokémon introduced in that generation as a pre-evolution to existing Pokémon (the other being Wynaut). Azurill was a new pre-evolved form of Marill (which itself was introduced in Generation 2, Gold & Silver).
Marill, looking very cute and less distressed
Like any other Pokémon that can be either male or female (which is most of them), there is a predefined gender ratio, which determines how likely you are to find that Pokémon of that gender in the wild. So a Pokémon species with a 50/50 male/female gender ratio (like Bagon and countless others) is equally likely to be male or female if you encounter one in the wild. Game Freak later make insidious use of this mechanic with Pokémon such as Salandit in Generation 7 (Sun & Moon). Only female Salandit evolve into Salazzle, but only 11.9% of wild Salandit are female. (Male Salandit just don’t evolve.)
Azurill has a 75% chance of being female and a 25% chance of being male. Interestingly, Azurill is also the only Pokémon that has a different gender ratio from any of its evolutions. Both Marill and its evolved form Azumarill are 50/50 male/female. A strange side effect of this difference meant that 1/3 of female Azurills evolved into male Marills.
He saw this coming
This is because of the way that a Pokémon’s gender is determined and stored in the games. Instead of storing the gender an individual Pokémon has with that Pokémon, its gender is instead based off of its personality value. That personality value is then used to look up its gender based on the ratio of its species. For the 25% of female Azurills that are between the 50 and 75 marks of their gender distribution, that lookup suddenly returns male when run against the 50/50 distribution for Marill.
Unfortunately for Azurill’s gender swapping history, Game Freak changed this behavior in Generation 6 (X & Y), so female Azurills now always evolve into female Marills. But it did remain that way for 3 generations (approximately 10 years)!
This particular edge case isn’t one that has tripped me up in PokémonCompDB, because I don’t (yet) generate databases for generations prior to Generation 6. Instead, it’s one that came up as interesting trivia while I was doing other research.