Lava Cookie is an item that is able to cure any status effect from a hurt Pokémon, including Poison, Paralysis, Burnt, Confusion, Frozen, etc. This item was introduced in Generation III and is Mt. Chimney's specialty.
In the Hoenn region games, this item can be found on Mt. Chimney. While in Pokémon FireRed and LeafGreen, a Lava Cookie can be found on Two Island. In the Sinnoh region games, the Lava Cookie can be found at Valor Lakefront or can be bought at the Veilstone Department Store. In Pokémon HeartGold and SoulSilver, this item can be found on the Volcano Path. Finally in Unova, this item can be found as a Royal Unova gift. In Alola, if you are lucky, the guy in one of the Pokemon Centre Cafe will give you one.