Pokémon Forms are a staple of the Pokémon franchise and involve different appearances, as well as sometimes types and stats of various Pokémon. While some of these Pokémon forms are changed by using moves, such as with Aegislash and Meloetta, most forms are actually unique and can't be changed. In order to get them, you have to go to the Pokémon stages multiple times with the hope of getting the Pokémon.

As it's random, and some are bosses, the drop rate is low so multiple attempts will be required, especially for Pokémon such as Arceus with multiple forms.

There is a reason to do this, however. Half a dozen of the Pokémon: Furfrou, Vivillon, Deoxys, Genesect, Unown, Kyurem, Giratina and Arceus have got special titles that are unlocked when you see and when you capture each of the forms. These may seem superfluous, but when you get the Master titles, you will unlock a special frame or outfit for your Mii's Profile.