Complex sentence: A huge rock formation is discovered beneath the surface, and is transported back to our planet, on which the seemingly-harmless rock grows into a colossal floating saucerlike crustacean life-form called "Negadon," which proceeds to attack Tokyo.
Split into simpler sentences: A huge rock formation is discovered beneath the surface, and is transported back to our planet. The seemingly-harmless rock grows into a colossal floating saucerlike crustacean life-form called "Negadon," which proceeds to attack Tokyo.