A crash star is an item from Bayouland in Videoland. It has the power to de-digitalize (i.e. destroy) hostile creatures.
When Dr. Wily sent a Swamp Creature to Bayouland to eat Kevin Keene, it shorted out his Zapper with swamp water. While Bayou Billy distracted King Hippo and Eggplant Wizard, Kevin used the skills Bayou Billy had taught him to reach a crash star. When he threw it, it destroyed the Swamp Creature and the snakes that were slithering after him, then followed King Hippo and Eggplant Wizard through a warp to Metroid and de-digitalized the two of them along with Dr. Wily and Mother Brain.