The Star Rod is a highly powerful item that Kirby needs to battle the evil Nightmare at the end of Kirby's Adventure, along with several other games. Its power involves the ability to shoot small stars rapidly at enemies and is often involved within the final battle(s) of Kirby games. The Star Rod also features as an item in the Super Smash Bros. series. Another funtion is powering the Fountain of Dreams by causing the magic waters to flow from it, giving the inhabitants of Dream Land their dreams.
WARNING: May contain spoilers!
The Star Rod is used to help defeat Nightmare in the final episode. When Tiff throws Kirby his Warp Star, Kirby instead swallows it to gain the ability. Kirby then proceeds to release a huge attack of stars, destroying Nightmare once and for all.