Movie sequels can be tricky things. Sometimes, movie number two is better than the original, but sequels can threaten to undermine the self-contained perfection of the first film. That's ultimately why we never saw a sequel to E.T.: The Extraterrestrial, although that doesn't mean Steven Spielberg never thought about it. His 1982 treatment for the E.T. sequel would have brought evil aliens into the mix.
In 1982, Spielberg and E.T. writer Melissa Mathison wrote a nine-page treatment of E.T. II: Nocturnal Fears, which is available online. Set a few months after the events of the original movie, the sequel would have followed Elliott, Gertie, and Michael, who formed an intense bond as a result of their experiences with E.T., but have become obsessed with the idea that their alien pal might return. Dr. Keys, the government agent from the original film, is dating their mom and, influenced by E.T.'s goodness, has decided to pursue a career in medicine. However, the next aliens to land on Earth aren't E.T.'s benevolent folk, but their mutant enemies:
The aliens onboard are EVIL. They have landed on Earth in response to distress signals designating its present coordinates. These aliens are searching for a stranded extraterrestrial named Zrek, who is sending a call for 'Help.'
The evil creatures are carnivorous. Their leader, Korel, commands his crew to disperse into the forest to acquire food. As the squat aliens leave the gangplank, each one emits a hypnotic hum which has a paralyzing effect on the surrounding wildlife. These creatures are an albino fraction (mutation) of the same civilization E.T. belongs to. The two separate groups have been at war for decades!
Yeeeeah. Not exactly the simple and magical story we fell in love with. Fortunately, in an interview with the American Film Institute, Spielberg acknowledged the perils of making a second E.T. movie:
Sequels can be very dangerous because they compromise your truth as an artist. I think a sequel to E.T. would do nothing but rob the original of its virginity. People only remember the latest episode, while the pilot tarnishes.
'E.T.' 30th Anniversary: The Sequel That Never Was and Three Decades of Cameos [Hollywood.com via Slice of SciFi]