Contrary

Full effect

Whenever this Pokémon's stats would be raised, they are instead lowered by the same amount, and vice versa.

In game description

Reverses any stat changes affecting the Pokémon so that attempts to boost its stats instead lower them—and attempts to lower its stats will boost them.

Using Contrary in Cobblemon

Abilities are passive and always active, so Contrary 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.