Gender differences were first introduced in Pokémon Diamond & Pearl, but as of Pokémon GO Version 1.27.2/0.57, gender has now become a factor into Pokémon. Most Pokémon have a gender, though some are exclusively male, exclusively female, and some lack a gender. There are, however, multiple Pokémon that have different appearances based on gender. These are purely aesthetic differences and appear in all facets of the game, but if you caught them before the update to Version 1.27.2, they will appear as male only..

Male	Female

The following Pokémon have gender differences: Venusaur, Butterfree, Rattata, Raticate, Pikachu, Raichu, Zubat, Golbat, Gloom, Vileplume, Kadabra, Alakazam, Doduo, Dodrio, Hypno, Rhyhorn, Rhydon, Goldeen, Seaking, Scyther, Magikarp, Gyarados, Meganium, Ledyba, Ledian, Xatu, Sudowoodo, Politoed, Aipom, Wooper, Quagsire, Murkrow, Wobbuffet, Girafarig, Gligar, Steelix, Scizor, Heracross, Sneasel, Ursaring, Piloswine, Octillery, Houndoom, Donphan, Torchic, Combusken, Blaziken, Beautifly, Dustox, Ludicolo, Nuzleaf, Shiftry, Meditite, Medicham, Roselia, Gulpin, Swalot, Numel, Camerupt, Cacturne, Milotic & Relicanth

Alolan Forms were introduced in Pokémon Sun & Moon with Galarian Forms following in Sword & Shield and Hisuian in Legends Arceus. In Pokémon GO, these Pokémon only appear during special Events or when you receive a 7km egg from a friend through Gifts. These Pokémon have different moves and types

Unown is one of the more unusual Pokémon with there being a total of 28 different forms. These forms take the appearance of the English alphabet, as well as an ! and ? Unown. These are determined randomly when Unown appears in Pokémon GO.

Not much differs between the Unown, but there is a special medal for collecting them.

Castform is a unique Pokémon in that it has forms that change depending upon weather. While in the main games, your Castform would change form in battle based on the weather, in Pokémon GO it is a bit different in that it is based on the weather you encounter it in and will not change after capture

Normal	Sunny Form	Rainy Form	Snowy Form
Cloudy Partly Cloudy Windy	Clear	Rain	Snow Foggy

The Christmas 2016 event introduced another version of Pokémon forms, special costumes for Pokémon. In this case, throughout the event Pikachu with a Christmas hat was seen in the wild for the duration of the event. This Pikachu was just like any normal Pikachu but wore a special hat, and kept the hat after the event. In addition to this, the hat was retained when Pikachu evolved into Raichu. This was then repeated for Pokémon's 21st birthday. On Pokémon GO's 1st anniversary, Pikachu was then given with Ash's hat from the original anime series. Raichu also could have the hat, but this time Pichu was also included. Hatched Pichu would have the hat. These continued on more and more with many events adding costumed Pokémon