Easter Eggs/ Reused Props I've Seen (that have not been mentioned here):
Not confirmed, but I feel like the Venkman at the end of Ghostbusters is wearing one of the Jack Torrance wigs from The Shining in 2017.
Shadowcreek Camps in Yeti (referencing the Havoc franchise).
I feel like one of the scareactors in Yeti had Marty's mask from Poltergeist last year.
The "Shining reference" in Us.
Old Smokey might be in the Rob Zombie zone but i'm not sure if its just some other chair.
The clown trashcan from Carnival Graveyard outside House of 1000 Corpses (maybe also the Bill and Ted Phonebooth).
The Skeleton Kid's mask from Trick'r Treat in one of the rooms of HOTC.
I think the girl in the cage in HOTC is wearing one of The Grady Twins dresses.
Something I noticed, three different scareactors in HOTC says "Who's your daddy" (also, someone skinned HHN Bear D:).
The Norris Thing in Depths of Fear.
"Infinite Pits" in both Depths of Fear and Universal Monsters (though they are harder to spot than usual).
Shield from 2005's Fire Pits in the Nightingales facade.
Feel like Nightingales eating horses is a callback to the original house.
Statues in the facade of Universal Monsters actually look like their original counterparts.
You are underwater in the Creature room.
There is a crypt named Hugo in the Wolfman room that might be a reference to Victor Hugo.
Graveyard Games used alot of costumes and sets from Poltergeist.
It also had a moving coffin from Hive.
The Mother character appears three times in Graveyard Games.
Alot of props from the Killer Klowns house are reused from the scarezone (naturally).