Stench
Has a 10% chance of making target Pokémon flinch with each hit.
Full effect
This Pokémon's damaging moves have a 10% chance to make the target flinch with each hit if they do not already cause flinching as a secondary effect. This ability does not stack with a held item. Overworld: The wild encounter rate is halved while this Pokémon is first in the party.
In game description
By releasing a stench when attacking, the Pokémon may cause the target to flinch.
Pokemon with Stench
Using Stench in Cobblemon
Abilities are passive and always active, so Stench 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.