The following is a partial list of film, television, literary, and video game properties that have been adapted over the years in Orlando; being owned by Universal Studios, the park has had access to many properties to turn into houses and scarezones. Some of these may not seem like traditional properties, but they can be quite effective....
Dyeing for Your Art: Many scareactors and show actors have had to undergo physical changes for their characters, but the most extreme example may be for Orlando in 2010's Havoc: Dogs of War and its 2013 sequel Havoc: Derailed, where every actor (male and female) shaved their head bald to play psycho super soldiers.
When the 2002 event, Islands of Fear, was held in the Islands of Adventure part of Universal Orlando, Dr. Seuss' widow Audrey Geisel vetoed attempts to host a scarezone in the Seuss Landing area of the park, feeling that it would be a disgrace to Seuss' family-friendly work and threatening to end the Seuss estate's partnership with Universal if it did so. They ultimately settled on Boo-Ville, a Lighter and Softer Halloween area that did not have any scareactors.
Promoted Fanboy: Many of the A&D members at Universal Studios in Orlando and Hollywood that helm the events started out as mere Scareactors/huge horror fans.
Prop Recycling: Very common, to the point of fans trying to identify what other houses and scarezones the props have been used in. Being Universal, they also get to use some movie props (such as a piece from Van Helsing). Props from former attractions like Kongfrontation and Ghostbusters Spooktacular are even sometimes used.
Too Soon: The reason why both Eddie and Cindy never came to be as icons. Universal was afraid Eddie would be considered too violent in light of the 9/11 attacks, so he was cut and Jack, a more fantasy-kind of villain, was brought back instead. With Cindy, she was cut due to child murders that had been happening around the area at the time.
What Could Have Been: Many icons, houses, scarezones, and event concepts have been scrapped over the years; infamous examples include Eddie, the chainsaw-wielding horror movie addict who was changed into Jack's brother, then dumped completely due to the 9/11 attacks, Cindy being replaced by The Caretaker after a rash of child kidnappings, and an almost-finished extreme house, Extreme Fear, in 2003 that was scrapped due to fear of litigation just before the event (see below).
Eddie would reappear with other icons in the Horror Night Nightmares house in 2006 and in the Horror Nights: The Hallow'd Past house & Fear Revealed scarezone in 2010. He received his own house, RUN: Hostile Territory (a sequel to the 2001 house RUN he was originally supposed to appear in) in 2006. The original RUN was intended to be his house before he was scrapped from the toned down event. In his original incarnation as Edgar Sawyer, he would have pulled a Hostile Show Takeover and killed Jack in the Opening Scaremonies. Whether Jack would have stayed dead is another story with how many times Edgar had to try before it stuck.
Cindy's case is interesting, as she had a cameo in Scream House: Resurrection in 2006 and her own house, The Orfanage: Ashes to Ashes in 2010. However, Universal was considering having her be the icon for the 2010 event and aren't against the idea of having her as an icon in the future.
Concepts for an "extreme house" (a house in which, with full permission, visitors would be taken through more intense scares and scareactors would be allowed to break the cardinal rule: no touching the guests!) have been brought up for the Orlando event for quite some time. The most concrete example of this was the "Severe Fear" house for HHN 13 that was scrapped at the very last minute due to fear that someone might get injured and sue the park. The full treatment and construction documents can be found here. Elements from this house treatment (the door scene, the use of live flame in a house, a chainsaw wielding drill sergeant, etc.) would be reused in future houses and scarezones.
Many Icon concepts are gone through before Univeral A&D finalizes the Icon to be used for the event. Most of these are lost to the archives but some of them eventually get used in some way, shape, or form. For example, Jack's girlfriend Chance actually had her origins as the Icon concept, Jack's EX-girlfriend Jill, in an event that would span both the main park and Islands of Adventure. Lady Luck had her origins in an earlier Icon concept as well.
Supposedly, the 2012 house Gothic, set in a medieval cathedral filled with menacing gargoyles, is based on a canceled room concept for an old house.
Many of the masks worn by the Beasts in 2012 were based on the masks of older characters, but several of them were a more unique design. Rumor has it that these masks were part of a canceled house based on the Chupacabra.
An American Werewolf in London was set to be a house in two previous years, believed to be 2008 and 2012, and came close enough to completion that props and sets had to be scrapped or retooled. 2013 was when John Landis finally gave personal approval.
A common fan discussion is on the viability of Universal's new Harry Potter attractions for HHN, with the common statement being that J. K. Rowling has barred the use of her properties for such uses (to the point that Diagon Alley is closed to the public during HHN Orlando from 2014 onwards). According to some, Rowling actually approves of the series being used for an adult event and the only obstacle is the corporate side....
2008's house Creatures! was a fun, campy house inspired by EC Comics. Set in a Southern roadhouse called the Butchered Buck, the house chronicled the battle between a group of rednecks and goofy-yet-scary aliens◊. That's all well and good. The problem? The alien costumes were too large and cumbersome and were deemed to be a safety hazard shortly before the event begun. With the exception of one creature seen behind a fence, there were nearly no creatures in the house called "Creatures".