“Science transformed him into a monster. Love changed him even more!” Swamp Thing, a Wes Craven movie released in 1982, was more sci-fi than horror, but we include it here. The movie received mixed reviews, although they were weighted more on the positive side. The movie did up being profitable, and a low budget sequel, The Return of Swamp Thing, was released in 1989.
In the original movie, a government agent, named Alice Cable, is sent to guard Dr. Alec Holland, who is developing some kind of weird plant/animal concoction in the swamp lands of Louisiana. The formula is meant to create animal/plant things that can thrive in harsh conditions, in the hopes to end world hunger. Holland's arch enemy, Anton Arcane, comes to steal the potion, and then decides to douse Holland with it.
What happens? Holland turns into a walking weed. But this weed has powers, and he is hell bent on saving the beautiful Alice from his Anton. In the end, Holland is able to battle Anton’s forces and even Anton himself, who has also mutated into some type of strange creature after having misappropriated the secret formula.