Bad Dreams
Damages sleeping opponents for 1/8 their max HP after each turn.
Full effect
Opposing Pokémon take 1/8 of their maximum HP in damage after each turn while they are asleep.
In game description
Damages opposing Pokémon that are asleep.
Pokemon with Bad Dreams
Using Bad Dreams in Cobblemon
Abilities are passive and always active, so Bad Dreams 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.