Slow Start

Full effect

This Pokémon's Attack and Speed are halved for five turns upon entering battle. This ability also takes effect when acquired during battle. If this Pokémon loses its ability before the five turns are up, its Attack and Speed return to normal; if it then regains this ability without leaving battle, its Attack and Speed are halved again, but the counter keeps counting from where it was.

In game description

For five turns, the Pokémon's Attack and Speed stats are halved.

Using Slow Start in Cobblemon

Abilities are passive and always active, so Slow Start 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.