Undergrunt Gunner is a boss in Super Mario Galaxy and a regular enemy in Super Mario Galaxy 2, serving as regular flying cannons around Bowser and Bowser Jr.'s defenses that appear in both Super Mario Galaxy games. They appear to be based off of Water Shooters, Fire Cannons, and Electric Pressures.
Super Mario Galaxy
Gold Leaf Galaxy
In Gold Leaf Galaxy, the mission is called "When it Rains, it Pours." One of the Bees complained to Mario that the "mean mole" took their deck. In the battle, Undergrunt Gunner is shooting bubbles. To beat him, the player must avoid bubbles by going behind the wall. Bee Mario can fly over him and pound on the glass to attack him. He is still vulnerable when playing as normal Mario, when jumping further. The longer Mario stays on top off him, the more his rage and spinning will increase. When enraged, he shoots bubbles rapidly. After finished off, his machine explodes resulting the Power Star to be given.
Toy Time Galaxy
He now uses the electric machine that causes damage and he is on a higher level making it difficult ground pounding his machine. Mario should use the Spring Mushroom to jump higher and then Mario can ground pound him. This should be repeated three times to be rewarded the Power Star.