Pokémon Mystery Dungeon: Explorers of Time and Explorers of Darkness/Chapter 19: To the Hidden Land

The hidden land is full of very powerful pokemon that can really stinge you from the get-go. Dragonite, Garchomp, Rampardos, and Bastiodon will be some of the pokemon you face. There are two parts of this place. After you get through both places, you will face Dusknoir and five Sableye. Use moves that hit everything, like Discharge. Make sure you have Reviver Seeds.