Brain Busters are levels in Plants vs. Zombies 2 which are more challenging than usual levels and also add different mechanics, conditions, or objectives to gameplay. They are marked on the map as semi-spheres with striped icons, instead of solid colored semi-spheres like regular levels. In the Chinese version and before the 1.7 update, these were unlocked using world-specific keys. Some Brain Busters are remakes of Plants vs. Zombies mini-games, but most of them are new. Gameplay wise, they play out similarly to the mini-games and puzzles of the first game. Some Brain Busters are exclusive to one world.