Ben 10 season 2 episode 2 : The Big Tick

During a trip to Yellowstone National Park, Ben discovers a new form on the Omnitrix: Cannonbolt, an armadillo- and beetle-like alien. At the same time, a meteor crashes nearby unleashing a giant, tick-like alien called the "Great One" that intends to devour the planet. On top of that, it has its very own worshipers, who intend to make sure it completes its task. Ben easily defeats the worshippers, but the Great One is impervious to all of his original alien forms. Since nothing else works, Ben has to rely on a form he knows nothing about in order to defeat the Great One. He quickly discovers that Cannonbolt is impervious from any attack when rolled into an armored ball and penetrates the Great One's armor in that form, killing the alien from the inside. The worshipers proclaim Ben the new Great One, but change their minds once he reverts back to normal.