Behind Chain Chomp's Gate is the final mission of
Bob Omb Battlefield.
Mario must start by making his way to the Chain Chomp. Then, Mario must ground pound the log holding down the Chain Chomp three times. He has to be very careful, though, as the Chain Chomp will try to attack Mario while he is doing so. Upon successfully ground pounding the log three times, the Chain Chomp will be freed and he will break the gate blocking the Power Star.