Great One

The Great One is a giant, tick-like alien that travels from world to world, sucking the energy from the planets it lands on to feed itself. This process poisons and eventually makes the worlds it visits implode. Its shell is nearly impenetrable as Grandpa Max and Gwen used its fallen shells to fend The Great One's followers attacks(which didn't even scratch the shells). Also, none of Ben's aliens were able to break it until he finally used Cannonbolt to destroy it from the inside after it shed some of his shell. It was shown to have two arms that can fire lazers powerful enough to send Ben (who was Four-Arms at that moment) crashing to the the ground before the Omnitrix timed-out. The Great One also secretes gooey liquids while shedding, some of which are acidic. Its feeding process causes the landscape to mutate as an extra defense, making it very difficult to attack. On top of that, it is followed by a group of worshipers that want to make sure that it completes its task. The Great One is destroyed from the inside by Ben as Cannonbolt. It is also responsible for the complete destruction of Cannonbolt's home planet about a week before it tried to destroy Earth, a somewhat ironic accomplishment considering its death at the hands of a member of the same species. The Great One also appeared along with the Leader Alien, the Enforcer Alien, and the Interpreter Alien.