Voltron: The Beast King Go-Lion Season 1 Episode 18

A Glara scientist shows Prince Imperial Sincline a new potion which can turn plant life into killer beasts. Sincline is then informed that his father, Emperor Diabazaal, is very sick and near death. Honerva tells Sincline that only the blood of a human female can save his father. Sincline then travels to Altea with the scientist's potion which he plans to use to create Deathblack Bestmen out of a few trees and use the Beastmen to capture young women to be killed for their blood.