Arena Openers are a tank created by X5163x. Arena Openers spawn from Arena Closers after they close the arena. They shoot blue or red circles with a gray barrel when a tank wants to join. When they are touched, they turn into Arena Closers and close the arena.
If nobody wants to join and they die in FFA or TDM mode, the arena will never be closed until there are no players in there. In Domination and Mothership mode, the Arena Closers will respawn.