Rattled

Raises Speed one stage upon being hit by a Dark, Ghost, or Bug move.

Full effect

This Pokémon's Speed rises one stage with each hit from a damaging Dark-, Ghost-, or Bug-type move.

In game description

The Pokémon gets scared when hit by a Dark-, Ghost-, or Bug-type attack or if intimidated, which boosts its Speed stat.

Pokemon with Rattled

Using Rattled in Cobblemon

Abilities are passive and always active, so Rattled 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.