The Stanley Dynamic Season 3 Episode 23 The Stanley Monster

Luke accidentally drinks Morgan's plant growth serum, and the side effects turn him into a petulant teenager. Seeing an opportunity to become the "good son" in his parents' eyes, Larry brews a modified version of the serum, which accidentally turns Luke into a monster. Meanwhile, Dad is mistaken for a substitute teacher at the high school, and manages to impress Principal Webber.