Innards Out
When this Pokémon faints from an opponent's move, that opponent takes damage equal to the HP this Pokémon had remaining.
In game description
Damages the attacker landing the finishing hit by the amount equal to its last HP.
Pokemon with Innards Out
Using Innards Out in Cobblemon
Abilities are passive and always active, so Innards Out 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.