Battle Frontier was the forth opening for Pocket Monsters Advanced Generation and it featured a few variants throughout its run and was used as an ending on Pokémon Sunday from PS053 to PS059. A special variant featuring Mystery Dungeon was also broadcast around the time the games were released in Japan.
The original variant starts off with the Battle Frontier symbol floating in space as some of the frontier brain symbols flying into it. The Pocket Monsters Advanced Generation logo scrolls in from the sides and gradually gets bigger. The next scene features Satoshi and Pikachu running down a hill until they get near the bottom and then jump into the air.
The following scene features all the main characters and their Pokémon camped out for the night as Takeshi cooks their dinner in a big pot on an open flame. Masato runs around as Haruka's Zenigame runs around and chases him. The video scrolls to the right until Haruka shows up resting against the truck of a tree but seems sad and has tears in her eyes.
Hanako, Professor Okido, Professor Odamaki, Kenji and Kasumi have quick appearances together as the video scrolls up to show them. Satoshi's Pokémon in their current evolutions during the airing of the opening are shown. Different variants of the opening have different stage evolutions of his Pokémon. Pikachu is the last Pokémon to be shown and he uses his Thunderbolt in a forest causing a huge explosion with smoke flying everywhere.
Enishida drives by in his car and waves as silhouettes on the Frontier Brains are shown. Different variants of the opening reveal the silhouettes of the Frontier Brains as Satoshi encounters them in the series. Rocket Gang make their appearance in the anime with their Pokémon as they wave back and forth until they look to their left to see a Mew flying in the air. It passes a tree where a Lucario is standing. The song ends with silhouettes of the main characters appearing and then colorizing as they pose together.