Evolution is when Pokémon change form. There are many different ways this happens:
- Leveling-up
Sometimes when a Pokémon levels up it evolves. To grow levels, your Pokémon must get a certain amount of experience points (EXP). Obviously the only way to do that is to have it participate in battle (EXP share also works).
- Trading
Using a GBA link cable you can trade certain Pokémon to other trainers. Some Pokémon evolve when this happens.
- Items
When some Pokémon are given items they evolve.
- Trading with items
Rare items are known to evolve Pokémon, but only if they are traded with the item.
- Stones
Leaf, Sun, Moon, Fire, Thunder and Water Stones also evolve Pokémon, but these are rare.
- Random
Random evolution occurs when one Pokémon may turn into one of two different Pokémon.
- Specific conditions
When it doesn't fit one of the other categories, it is considered a special condition.
- Taming
When Pokémon are happy enough, they might evolve. In Verdanturf Town there is a lady who can rate your Pokémon's happiness.
- Spectral
Once one Pokémon becomes two, it enters this category.
- Combination
If it fits two or more categories it goes here.