Hi Pauly88, all you need is Cousin It and the Thing character to help flesh out that this is the Addams family house (I assume someone is dressing up as Tish or Gomez). Then in regards to decorating, just look at the song:
They're creepy and they're kooky,
Mysterious and spooky,
They're all together ooky,
The Addams Family.
Their house is a museum
Where people come to see 'em
They really are a scream
The Addams Family.
Have a house that looks a bit normal at first glance, but not so much when you take a good look.
A distressing welcome mat
A werewolf rug
Cabinet of curiosity items around the house
https://www.pinterest.com/zim2/halloween-cabinet-of-curiosities/
Some weird food items in the kitchen
Wednesday's play room with a creepy doll house and other toys
Maybe Wednesday has a "lemonade stand" out front but is selling poison drinks
A piranha fish tank
Lots of weird framed pictures on walls and tables
Here's a bunch of ideas:
https://www.pinterest.com/zim2/halloween-monster-house/
And here's a link to some of Addams family rooms -
http://www.huffingtonpost.com/2013/11/21/addams-family-photos_n_4316085.html
Big Lots has some fun horror home furnishings this year. You can pick up their TV, animated lamp with The Thing hand, movie projector and phone.
http://www.biglots.com/c/seasonal/halloween/_/N-2915497221
Target this year has a Nocturne collection with some creepy home items
https://www.target.com/p/halloween-...r-collection/-/A-52722421?lnk=NocturneCollect