Gathering the Gang of Four! - S9.E42

At the Fennel Valley Pokémon Center, Ash gets a special delivery from Oak's Lab—his Bulbasaur. Officer Jenny soon arrives with his Squirtle, and his Charizard flies in too. Ash is going on a retreat with these three Pokémon and Pikachu to train for his upcoming rematch with Brandon. Out in the forest, the four Pokémon work together to build a bed to sleep on, but Charizard hogs it at first and starts a fight. Eventually they calm down and rebuild the bed, get some food, and even practice their moves. That night Charizard lights a campfire, and Ash remembers how he met Pikachu, Charizard, Squirtle, and Bulbasaur.