List of Pokémon with different forms

Some Pokémon may appear in different forms during certain weather conditions or in certain regions. These Pokémon have some differences comparing them to regular ones of the species, such as different types, moves, base stats and height and weight.

Alolan forms
There are certain Kanto-region Pokémon that have different forms as they inhabit Alola region.

Unown
In case of Unown, there are no different types, moves nor statistics among any of its forms. Each of these forms resembles other letter of Latin alphabet with addition of exclamation and question marks.

Spinda
There are currently 20 different patterns for Spinda and additionally 20 another different patterns for its shiny variants in game data, which gives total of 40 different patterns for Spinda. 8 of these forms were released so far.

Castform
Castform can appear in different forms when spawns during certain weather conditions.

Shellos and Gastrodon
Shellos has two forms east sea(pink) and west sea (Blue)

Rotom
Rotom has six different forms that differ with its secondary types.

Giratina
Giratina has 2 formes, Origin form(no legs) and Altered form(legs).

Arceus
Arceus has 18 different forms depending on its type.

Trivia

 * On May, 2018, Alolan forms of Pokémon, originally discovered in the Kanto region, were stated to begin to appear in-game.