Azurill gender glitch

Miscellaneous glitches of Pokémon Ruby and Sapphire, Pokémon FireRed and LeafGreen and Pokémon Emerald

Exclusive to Ruby and Sapphire:
256x item selling price glitch | Amazing Trainers | Berry glitch | Draining hitpoints animation glitch | Evolution animation glitch | Sticky Hold glitch | Mossdeep City Skitty glitch | Truck glitch | Nightmare glitch | Mossdeep City Skitty glitch
Acro Bike instability glitches (Japanese only) | Dark red selector glitch (International only) | Excessive doll arrangement glitch (Japanese only) | Mail and Trick glitches (Japanese only) | Surf on land (Japanese only)

Exclusive to FireRed and LeafGreen:
Celadon City origin glitch | Pokédex species glitch | Roaming Pokémon Roar glitch

Exclusive to Emerald:
Battle Pike poison knockout glitch | Black curtains glitch | Mart worker glitch | Mover Vigoroth cry glitch (Japanese only)

In various or all entries:
Azurill gender glitch | Boss HP recruit glitch (Mystery Dungeon) | Decamark-specific glitches | Dewford Gym footprint glitch | Evolution move-learning glitch | Focus Punch glitch | Roaming Pokémon IV glitch | Sky Pillar glitch | Thunderbolt glitch | VBlank RNG interrupt glitch

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Bulbapedia also has an article about Azurill gender glitch.

The Azurill gender glitch is a recurring glitch; first existing in Generation III of the Pokémon games and later appearing in Generation IV within Pokémon Diamond, Pokémon Pearl and Pokémon Platinum. It is currently unknown whether this glitch still exists in Pokémon Heartgold and Soulsilver.

When a female Azurill evolves into a Marill there is a 1 in 3 chance (not taking into account possible error from the Pseudorandom Number Generator) that it will 'change' into a male Marill. This can be explained by the fact that the gender rate of Marill is different to that of Azurill. Whilst Azurill is 75% female, Marill is 50% male and female. The gender of a Pokémon is determined by its hidden personality value and a certain range of values will determine whether it is male or female. When Azurill evolves however, the possible range of values ensuring that Marill is female are reduced so there is a slight chance of a female Azurill evolving into a male Marill.

External links

1. [1] - A video of the Azurill gender glitch on Pokémon Ruby.
2. [2] - A video of the Azurill gender glitch on Pokémon Diamond and Pearl.