poison ivy --
Welcome to the thread!
Did you happen to read
figment_jii's comparison of the MHP vs.
MNSSHP (there is a link in the MHP FAQ on page 1 of this thread)? That may help clear things up a bit.
There isn't really anything overtly scary or frightening at the MHP. It's mostly all light and happy. The Cavalcade has characters and is upbeat and lively.
There are some spookier effects on the Big Thunder Trail and over the Rivers of America -- fog and eerie lighting -- but it stops there. You may want to avoid those spots. You will see colored lights and images projected onto various facades (including the Castle and It's a Small World), such as skeletons, spider webs or pumpkins, etc.
The area around the Hub will likely be crowded with people waiting for the Halloween Screams fireworks, so steer clear of that if you don't want to see the fireworks.
I would stay tuned to this thread for reviews of the MHP as they come in (after tonight) -- maybe that will help give you an idea of what is happening at the parties this year.
I would go to the treat trail in Pixie Hollow (very pretty at night) and maybe the treat trail at the Golden Horseshoe (for extra Halloween decorations inside the building).
If you're there in the daytime,
before the party, go to the Halloween Carnival to see the amazing carved pumpkins and various pumpkin figures around the area (as well as the petting zoo)