Pickpocket

Full effect

Whenever a move makes contact with this Pokémon, if it does not have a held item, it steals the attacker's held item. This Pokémon cannot steal upon being knocked out. It can steal if the attacker has a Substitute, but cannot steal when its own Substitute is hit. If a move hits multiple times, only the last hit triggers this ability. If this Pokémon is wild, it cannot steal from a trained Pokémon.

In game description

The Pokémon steals the held item from attackers that made direct contact with it.

Using Pickpocket in Cobblemon

Abilities are passive and always active, so Pickpocket 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.