Implement forms

[rhysm94]

Forms are different versions of Pokémon species which either simply look different (e.g. different Unown letters), or have different stats and/or different typing to their base, normal form.
This second kind of forms can be further subdivided into different categories. Some form changes are user activated, some activated by battle conditions, some forms are only changeable outside of battle, and some aren’t changeable at all (e.g. Alola forms)

Castform provides an example of a Pokémon whose form differences are activated by battle conditions. Its ability, Forecast, changes its type based on the weather:

• Normal Form (Normal type), activated by any weather not associated with a form
• Sunny Form (Fire type), activated by sunlight
• Rainy Form (Water type), activated by rain
• Snowy Form (Ice type), activated by hail

Some Pokémon have what’s known as an Alola form, a form that is only obtainable in Pokémon (Ultra) Sun and Moon. These forms are set, and may have different types, stats, and movesets from their non-Alola forms.

As a player, I want to either be able to choose a form before battle, or have the ability to change form mid-battle as per form-change requirements, to broaden the strategy involved and to bring the battle engine closer to replicating the cartridge’s battle engine