Complex sentence: Starro is an intelligent alien lifeform resembling a giant starfish with a central eye and prehensile extremities which, upon its first appearance, came to Earth and gave his powers to three starfish.
Split into simpler sentences: Starro is an intelligent alien lifeform resembling a giant starfish with a central eye and prehensile extremities. In his first appearance, Starro came to Earth and gave his powers to three starfish.