Pokémon Emerald was the first main-series Pokémon game to feature the Battle Frontier as a post-game facility.
Released for the Game Boy Advance in Japan in 2004, Emerald expanded on Pokémon Ruby and Sapphire. After the player defeats the Pokémon League Champion, the Battle Frontier becomes available as a large collection of specialized battle challenges.
The facility includes the Battle Tower from earlier games along with six new venues, each built around different rules or battle formats. Players earn Battle Points by completing challenges and can exchange them for prizes and useful items.
The Battle Tower itself predates Emerald, appearing in Pokémon Crystal and later games. The distinction is that Emerald introduced the broader Battle Frontier concept: a group of themed facilities gathered into one post-game destination. Pokémon Ruby had a Battle Tower, but not the full Battle Frontier. Later games, including Pokémon Platinum and Pokémon HeartGold and SoulSilver, introduced their own versions or related facilities.