An Ability is a special, passive trait that a Pokémon can have. Each Pokémon species can have up to three different possible Abilities—up to two possible ordinary Abilities in addition to one possible Hidden Ability, which requires certain conditions (these vary by Generation). Abilities were introduced in Generation III, in Pokémon Ruby and Sapphire. They have been present in every main series Pokémon game since then, with the exception of Pokémon Let’s Go, Pikachu and Eevee.
An individual Pokémon that has one Ability is generally unable to change it to any of its other possible Abilities, although there are items that exist that can change Abilities, such as the Ability Capsule (Generation VI+) and, for Hidden Abilities, the Ability Patch (Generation VIII+). As a result, if you catch or hatch a Marill with Thick Fat for its Ability, you would have to catch or hatch a different one to get one with Huge Power, unless you use the expensive Ability Capsule item.
What Do Abilities Do?
Abilities do all sorts of things. Again, they are generally passive effects on the Pokémon while it is sent out in battle, but some Abilities activate just when it is sent out while others activate only after certain conditions are met.
- Starter Pokémon all have Abilities—Overgrow, Blaze, and Torrent—that raise the damage of their respective type’s moves by 50%, but only if the Pokémon with the Ability has 1/3 or less of its HP remaining. There are also similar Abilities, such as Swarm.
- Some Abilities like Intimidate activate only when the Pokémon is sent out. That Ability lowers the Attack stat of each of the enemy Pokémon on the field when its user is sent out, making it very useful.
- Some Abilities activate different weather conditions when the Pokémon is sent out, such as Drought (sun), Drizzle (rain), Sand Stream (sandstorm), and Snow Warning (hail), while other newer Abilities change the Terrain, such as Grassy Surge (Grassy Terrain) and Electric Surge (Electric Terrain).
- Some Abilities grant immunities to different status conditions, such as Insomnia and Vital Spirit both preventing the Pokémon with the Ability from falling asleep, or Immunity preventing the Pokémon from getting poisoned. Other Abilities grant resistances or immunities to different types of moves, such as Levitate giving the user an immunity to Ground-type moves, or Flash Fire giving an immunity to Fire-type moves while also powering it up if it gets hit by one.
- Some Abilities even have their uses outside of battle, such as Pickup sometimes allowing the Pokémon to pick up some useful items after every fight (though, as of Generation V, it also has an in-battle effect to pick up certain held items consumed by the enemy), or Illuminate raising the encounter rate of wild Pokémon.
As you can hopefully see, Abilities are very useful and give all sorts of options to the Pokémon that have them. Having a good, useful Ability can make all the difference for a Pokémon’s usability.
By the way, not all Abilities are good! Some Abilities are actually a detriment to the Pokémon, such as Regigigas‘ Slow Start Ability, which halves its Attack and Speed for the first five turns that it has been sent out, or Slaking‘s Truant Ability, which prevents it from acting every other turn. These two Pokémon in particular have very high base stats to compensate for their bad Abilities, though.
Changing Abilities Upon Evolution
Sometimes Pokémon change their Abilities when they evolve or when they change forms. In the case of changing forms, this is a temporary change only while the Pokémon is in the different form, but for Pokémon that evolve, their change in Ability is permanent.
In the case of Pokémon changing their Ability upon evolution, and where both the original stage of the Pokémon and the evolved stage have differing Abilities, it will always change to the Ability in the same slot. For instance, Lillipup has Vital Spirit and Pickup for its normal Abilities, while Herdier has Intimidate and Sand Rush for its normal Abilities. When a Lillipup with Vital Spirit (slot 1) evolves, it will have Intimidate (slot 1), while a Lillipup with Pickup (slot 2) evolves, it will have Sand Rush (slot 2) instead.
It’s also possible for only one Ability of the evolved Pokémon to differ, and it is also possible for the evolved Pokémon to have just one Ability, in which case the unevolved Pokémon’s Ability won’t influence it.