Other mistake: When Rocky is in the funhouse looking at himself, he appears to look relatively "normal". But it's very obvious that it's got nothing to do with the mirror, and more to do with the removal of a lot of makeup. For example, Rocky usually has almost no nose, but in the mirror he has Eric Stoltz's very well developed nose.
Mask (1985)
1 other mistake
Directed by: Peter Bogdanovich
Starring: Laura Dern, Sam Elliott, Eric Stoltz, Cher, Estelle Getty
Deliberate mistake: The mirror that made Rocky's face look normal should've made his mom's face look different, but her face stayed the same.
Rocky Dennis: Don't worry, Mr. Simms. I look weird, but otherwise I'm real normal. Everything'll be cool.
Trivia: Rocky wasn't buried in a cemetery as shown in the end. His body was donated to science.
Answer: His official cause of death was listed as "sudden arrhythmic death syndrome," which is basically just when someone dies unexpectedly, usually during sleep. It's widely believed that it was caused by his disorder, as his disorder often causes early death, but to my knowledge it was never definitively proven.
TedStixon