A regular and welcome fall visitor to these parts, Ringling Bros. and Barnum & Bailey are a household name in circus entertainment. Yet despite the usual dazzling array of death-defying acrobats, exotic animals and colorful clowns, how do you up the excitement even more for this tried-and-true spectacle in family fun? This year, the answer seems to be that you take it to the extreme—the Circus XTREME, that is. A new show in the Ringling canon coming to the TD Garden October 13–16, Circus XTREME adds spectacular stunts from BMX trick riders, trampoline daredevils, bungee aerialists, a human cannonball and more into the mix of more than 100 international artists who make this “The Greatest Show on Earth.”