Pokémon Battle Frontier Episode 31 Grating Spaces! ( Air Date 2006-05-18 ) Genre Animation, Action & Adventure, Sci-Fi & Fantasy category. Overview "Upon arriving in Pewter City, our heroes learn that Brock's old Gym is being remodeled by none other than Team Rocket in disguise, and Brock and Ash must battle them to put a stop to it!".