Drizzle
Summons rain that lasts indefinitely upon entering battle.
Full effect
The weather changes to rain when this Pokémon enters battle and does not end unless replaced by another weather condition. If multiple Pokémon with this ability, Drought, Sand Stream, or Snow Warning are sent out at the same time, the abilities will activate in order of Speed, respecting Trick Room. Each ability's weather will cancel the previous weather, and only the weather summoned by the slowest of the Pokémon will stay.
In game description
The Pokémon makes it rain when it enters a battle.
Pokemon with Drizzle
Using Drizzle in Cobblemon
Abilities are passive and always active, so Drizzle costs you nothing to run. If it is marked hidden on a species above, expect it to be harder to obtain: servers differ in whether hidden abilities come from breeding, an Ability Patch, or events.
See the Pokedex for which abilities each species can have, and IVs, EVs and breeding for how to actually pass one down.