Pokémon's form and ability to be a "normal" Pokémon

[Celebri]

The title is confusing, I know, so allow me to elaborate.
I'm creating a berry Pokémon, that has different formes depending on which berry it holds in the wild. Like, if you meet its Blue Form, it will hold an Oran Berry, and if you meet its Pink Form, it will hold a Pecha Berry. I want this to be random though, so the player won't only meet its Blue Form in the wild. How do I make it so the player can meet any of its forms in the wild (besides making its different formes appear on different maps, like Shellos). It's a bit like Flabébé actually.

 

[WolfPP]

For v17.2 you need to create a code into _Form script. Check how Giratina's code works (when hold Griseous Orb) and try to create a code for your fakemons for wild encounters.