Tangling Hair
When this Pokémon takes regular damage from a contact move, the attacking Pokémon's Speed lowers by one stage.
In game description
Contact with the Pokémon lowers the attacker's Speed stat.
Using Tangling Hair in Cobblemon
Abilities are passive and always active, so Tangling Hair 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.