Hide and Seek or Southpark
I've been sick with a fairly bad cold the past few days, so I've probably watched around 50 hours of TV since Friday. Besides the obvious downsides of watching so much TV, I've also seen the commercial for the movie "Hide and Seek" around 100 times. Not only does that look a piece of crap movie (why deniro why?), it looks like a copy of an episode of Southpark. The one where Stan's Aunt Flo (who visits every month) gives Stan a goldfish that turns out to be a demonic killer from an alternate universe. ("I've got such a good boy" says stan's mother as she buries the fish's latest victim in the backyard)
Hide and seek has some writing appearing on a wall behind a bathtub, which to me looks just like the south park fish blowing on the aquarium wall, then writing spooky messages to Stan.
A quick google gives some secrets from the show.
The spookyfish part of the show has it's roots in The Bad Seed (1956), which is one of Trey Parker's favorite films according to that webpage.