Moody
Raises a random stat two stages and lowers another one stage after each turn.
Full effect
After each turn, one of this Pokémon's stats at random rises two stages, and another falls one stage. If a stat is already at 6 or -6 stages, it will not be chosen to be increased or decreased, respectively.
In game description
Every turn, one of the Pokémon's stats will be boosted sharply but another stat will be lowered.
Pokemon with Moody
Using Moody in Cobblemon
Abilities are passive and always active, so Moody 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.