I'll keep the spoiler tags, just in case, as I'll go into some details: Spoiler I did think of Basket Case but didn't mention it because Belial isn't really used as a plot twist in the same way. Whereas, EDT runs for about 2/3 of its run time as a straight-up giallo inspired slasher before the evil mutant twin is revealed. And the film gets quite bonkers after than point. So, the structure is very similar. And, if I remember correctly, the "host" twin is also unaware of the "mutant" twin killing people. Also, if you want to use spoiler tags you write the word "spoiler" in between [ ] brackets at the beginning and "/spoiler" in between [ ] brackets at the end.