Pokémon Diamond Version, Pearl Version, and Platinum Version - Form Changes
Some Pokémon species can change form during battle. At the end of a Pokémon’s attack segment, after an attack is used (before fainting if any, but not Pursuit as a target is about to switch), at the end of each turn, and whenever a Pokémon enters the battle (including when a battle begins), the following will occur:
- If a Pokémon’s current species is Cherrim, it assumes the Sunshine Form if Sunny Day is in effect, and the Overcast Form otherwise. (Affected by Cloud Nine and Air Lock.) This lasts until the Pokémon leaves the battle. However, these two forms appear to have no special effect in battle. (Outside of battle, Cherrim assumes the Overcast Form.)
- If a Pokémon’s current species is Shaymin in its Sky Forme and is frozen, it becomes the Land Forme and its current stats are recalculated according to, and its types and ability change to conform to, the Land Forme, using the Pokémon’s level and original IVs, whether or not Transform is in effect for the Pokémon. The Land Forme change lasts even after the battle ends.
- If a Pokémon’s current species is Giratina in its Origin Forme and actually doesn’t hold a Griseous Orb and isn’t in the Distortion World, it becomes the Altered Forme and its current stats are recalculated according to, and its ability changes to conform to, the Altered Forme, using the Pokémon’s level and original IVs, whether or not Transform is in effect for the Pokémon. (Note that during battle, the reverse is not true.)
- If a Pokémon’s current species is Castform and has Forecast, its current type becomes Fire during Sunny Day, Water during Rain Dance, Ice during Hail, and Normal otherwise, unless the Pokémon shares a type with that type. (Affected by Cloud Nine and Air Lock.) If the Pokémon changes its type this way (and only this way), its form changes to the form corresponding to its type. The type and form changes last until the Pokémon leaves the battle.
- If a Pokémon’s current species is Arceus and actually has Multitype, its color changes depending on the Plate held, or becomes normally colored if it isn’t holding a Plate. This change lasts even after the battle ends. However, this change in and of itself has no special effect in battle.
When a Pokémon uses Transform, it also takes on the target’s form. However, depending on the circumstances, this form can immediately change as described above.
When a Pokémon levels up, its original stats are recalculated to conform to the new level, using its original IVs, even if Transform is in effect for that Pokémon.