From Bulbapedia, the community-driven Pokémon encyclopedia.
There are a number of methods of evolution, which defines how and when a Pokémon evolves. These can make it slightly harder for some Pokémon to evolve in comparison to others.
Triggers of evolution
There are only three events that may cause a Pokémon to evolve:
- Leveling up
- Being exposed to an evolutionary stone
- Being traded
Of course, it is not sufficient that one of these events happens, but it is also neccesary that all the required conditions are met. Therefore, when we are speaking about a method of evolution, we mean both the event and the conditions. Which one of the evolution-triggering events must happen to make certain Pokémon reach its next evolution stage and what conditions must be met is determined for each Pokémon individually.
Pokémon from branched evolution families may evolve into different forms depending on the event that caused evolution and other conditions.
Evolving by level
This is the most common trigger of evolution: most Pokémon evolve when they level up. It is not neccessary that Pokémon levels up by gaining experience in a battle: Rare Candy will also trigger evolution if all conditions are met. However, leveling up in Daycare will not cause evolution. Also it will not evolve if it is holding an Everstone. If a Pokémon levels up in a battle, the evolution will be triggered immediately after the battle. Of course, there are no Pokémon that evolve by leveling up without any additional conditions.
Reaching a certain level
Amongst Pokémon that evolve by level, most Pokémon evolve as soon as they reach a certain level by leveling up. If a Pokémon is not able to evolve when it reaches the required level, it will try to evolve every time it levels up again. Therefore, Pokémon from this group cannot be evolved only if the somehow reached level 100 without evolving.
Example: Ekans evolves into Arbok at level 22.
This method of evolution in most cases has no special disadvantages. However, Meowth, for example, evolves into Persian at level 30, but learns Pay Day at level 32. In Generation IV Persian cannot learn Pay Day by leveling up, what means that if a player wants to have a Persian with Pay Day, he must not let Meowth evolve until it has learned this attack.
Some Pokémon evolve by leveling up if their hidden Happiness stat is 220 or above. It is usually true for baby Pokémon such as Cleffa, but also holds true for some other Pokémon, including Chansey (evolves to Blissey). This method of evolution was introduced in Generation II.
The following Pokémon evolve using this method:
Less common conditions
Knowing a certain move
Some Pokémon evolve when they level up if they know a certain move. All of them can learn required moves by leveling up. However, if they are made to forget these moves, they must relearn them in order to evolve with the help of move relearner. This method of evolution has been introduced in Generation IV.
Being in a certain area
This method of evolution has also been introduced in Generation IV games, where some Pokémon evolve when they level up in a certain area.
Holding a certain item
Some Pokémon evolve when they level up if they are holding a certain item. In this case the item disappears after the Pokémon evolves.
By time and happiness
Some Pokémon evolve by leveling up being happy, but only during a certain part of the day.
The following Pokémon are known to evolve this way:
With a certain Pokémon in the party
This is a unique condition: Mantyke evolves into Mantine when it levels up only if there is a Remoraid in user's party.
With high enough Beauty
This is also a unique condition: Feebas evolves into Milotic by leveling up if its Beauty stat is 170 or above.
With a certain gender and at a certain level
It is the third unique condition: Combee evolves into a Vespiquen if it is female. Male Combee do not evolve.
Some Pokémon from branched evolution families evolve into different forms depending on some additional factors. These factors are not conditions for evolution, since they do not determine the possibility of evolution, but what the Pokémon will become after evolution.
- Burmy. This Pokémon evolves at level 20, but its new form is determined by its gender and cloak (and cloak changes according to the place, where it has battled last time).
- Male Burmy → Mothim
- Female Burmy → Wormadam, but the type combination of Wormadam is determined by the cloak.
- With Plant cloak (after battling in the wild) → Bug/Grass Wormadam
- With Sandy cloak (after battling in a cave or on a beach) → Bug/Ground Wormadam.
- With Trash cloak (after battling in a building) → Bug/Steel Wormadam.
- Tyrogue. This Pokémon evolves at level 20 depending on its stats.
- Wurmple. It evolves at level 7 into Silcoon or Cascoon, depending on its personality value. This value is hidden, determined when Pokémon is caught and cannot be affected by the player. See the article about personality value for the exact formula.
- Shedinja. This Pokémon appears in the player's party when Nincada evolves into a Ninjask (at level 20) if there is a free space there (in Diamond and Pearl the player must also have a free Poké Ball). If there is no room for Shedinja, it will not appear (but Nincada will still evolve).
Espeon and Umbreon are not listed here, because they were already mentioned.
Evolving with evolutionary stone
Some Pokémon evolve when they are exposed to an evolutionary stone. The stone may be applied at any time, thus causing an instant evolution.
However, as the player can decide whether and when to evolve his or her Pokémon (although he always can decide it, since evolution can be cancelled or prevented by using an Everstone), he or she must take the decision carefully: most Pokémon will no longer be able to learn certain moves when they evolve in this way, and some (like Raichu) cannot learn any moves by leveling up, although there are exceptions to this rule and certain moves are exclusive to the stone-evolved Pokémon.
Usually there are no special requirements for stone-induced evolution, with only two exceptions:
Both Pokémon have other ways of evolution that do not depend on their gender:
Note that sometimes (in Bulbapedia as well) Oval Stone is said to be an evolutionary stone, because it is a stone and it is required for an evolution. However, technically Oval Stone is an evolution-inducing held item, which Happiny must be holding to evolve into Chansey when it levels up.
Evolving after being traded
Many Pokémon evolve only when they are traded. The evolution starts immediately after the trade, regardless of the method of trading used. However, sometimes there are additional conditions.
A well-known mistranslation in the Generation I games suggested that after trading a man a Raichu, he said that it had evolved. This fueled speculation as to whether or not there would be a third stage to the Pikachu line in Generation II; the third stage was realized in the form of a Baby Pokémon, Pichu.
Holding a certain item
Some Pokémon evolve when traded only if the are holding a certain item. Like any evolution-inducing held item, the item disappears after the Pokémon evolves.
The following Pokémon evolve using this method: