Abilities

Every pokémon has one ability. It's a fixed effect that always works, in every fight, without you pressing anything. Some only wake up with a certain weather. Others change damage, defense or catching.

Where the ability comes from

Each family (the whole evolution line) has three possible abilities:

Slot	Chance when caught
Common 1	49%
Common 2	49%
Hidden	2% (1 in 50)

The hidden ability only comes from catching on a hunt. In an egg, the ability comes from the mother (see below).
Pokémon from other sources (chests, the Sortuda, fossils, raids, the Boss Room) get one of the two common ones.
Evolving doesn't change the ability. The list belongs to the whole family.
The hidden ability shows on the sheet with the (hidden) tag.
Pokémon you already had before abilities arrived get one of the two common ones, never the hidden one.
You can't change a pokémon's ability. Want a different one? Catch or breed another.

Who has abilities in a fight

Fight	Who has abilities
Hunting, Boss Room, floor boss, raid	Only your team. Wild pokémon, bosses and raids fight without
Arena, Cup, duel	Both sides

The 21 abilities

The six weather abilities

Ability	What it does
Swift Swim	In rain: attacks 25% more often
Chlorophyll	In harsh sun: attacks 25% more often
Sand Rush	In a sandstorm: attacks 25% more often and doesn't get tired (in the Arena and the Cup, doesn't lose HP to the sandstorm)
Snow Cloak	In a blizzard: dodges 20% of damaging moves and doesn't get tired (in the Arena and the Cup, doesn't lose HP to the blizzard)
Compound Eyes	Never misses in fog. Outside fog: +5 points of crit
Lightning Rod	Electric damage taken −50%. In a thunderstorm: no Electric damage at all

"Attacks 25% more often" means move cooldowns drop to 80% while that weather lasts.

The catching one

Ability	What it does
Sand Trap	In a sandstorm: catching is 15% easier for the whole team. One pokémon with it on your active team is enough

The combat abilities

Ability	What it does
Blaze	At 1/3 HP or less: Fire moves ×1.5
Torrent	At 1/3 HP or less: Water moves ×1.5
Overgrow	At 1/3 HP or less: Grass moves ×1.5
Swarm	At 1/3 HP or less: Bug moves ×1.5
Intimidate	Every wave of enemies that comes in gets −25% Attack for 12 s. Doesn't stack
Thick Fat	Fire and Ice damage taken −50%
Sturdy	At full HP, a hit that would knock it out leaves 1 HP. Works again every time HP is full again
Levitate	Takes no damage from Ground moves
Regenerator	Recovers 0.4% of max HP per second
Rough Skin	Returns 8% of damage taken to the attacker. Stacks with Rocky Helmet up to 30%
Technician	Moves with power 60 or less deal ×1.5
Adaptability	Same-type moves ×2 (instead of ×1.5)
Super Luck	+10 points of crit (the crit cap is still 80%)
Poison Point	Anyone who hits it has a 20% chance to get poisoned (1% HP per second, for 6 s)

In the Arena and the Cup, Intimidate works for both sides: your intimidator lowers the enemy team's Attack when it comes in, and theirs lowers yours.

Abilities that only come as hidden

Adaptability and Sand Trap never show up in the common slots. They only exist as hidden abilities, 1 in 50.

Snow Cloak, Lightning Rod, Blaze, Torrent, Overgrow, Swarm and Poison Point are the opposite: they only show up in the common slots.

A few examples

Family	Common 1	Common 2	Hidden
Magikarp	Swift Swim	Intimidate	Adaptability
Horsea	Torrent	Swift Swim	Adaptability
Sandshrew	Sand Rush	Sturdy	Sand Trap
Pikachu	Lightning Rod	Technician	Adaptability
Bulbasaur	Overgrow	Poison Point	Regenerator
Charmander	Blaze	Intimidate	Chlorophyll
Squirtle	Torrent	Swift Swim	Regenerator
Swinub	Snow Cloak	Sand Rush	Sturdy
Gastly	Levitate	Super Luck	Regenerator
Eevee	Technician	Intimidate	Super Luck
Dratini	Intimidate	Rough Skin	Adaptability
Larvitar	Sturdy	Sand Rush	Rough Skin

Abilities in eggs

The ability comes from the mother: the parent that gives the baby its species. With Ditto, it's the other parent. Ditto never passes an ability.

The mother has	The baby hatches with
A common ability of the family	80% the same one. 20% a random pick between the two common ones
The hidden ability	60% the hidden one. 40% a random pick between the two common ones
An ability from another family	A random pick between the two common ones

Since the 20% random pick can also land on the same one, a mother with a common ability passes hers on 90% of the time.
The father's hidden ability doesn't pass. To build a line of hidden abilities, the hidden one has to be on the mother.
Eggs never roll a new hidden ability: the 1 in 50 chance only exists when catching.
No catalyst changes the baby's ability.