@Ryan who says a battle arena can't be the same area as one found in the game? the Adventure Time areas do that. (and I think the Holo-Pearls would be easier to make into minifig form than the gem mutants) I could also see possible ideas for the battle arenas based off the Lunar Sea Spire or the Gem Battlefield with pyramids as bases, and the Sky Spires from Giant Woman for Pearl and Amethyst's