This isn't particularly a mystery yet, but I'd like to bring attention to it and make it one.
October 2002. Universal Studios Florida puts on their yearly Halloween Horror Nights attraction, where their parks get a makeover at night, with haunted houses, scare zones and roaming scare actors. This event wasn't as big or as highly budgeted as it is these days, so they made do.
This particular year, Universal put on Maximum Carnage - a Marvel-themed haunted house centered around the psychopathic symbiote villian Carnage, a Spider-Man villian. The entire Islands of Adventure section was rethemed into Island Under Siege, a dark, alternate take where the villains won, and the heroes were dead, leaving villians such as Crossbones and Silver Samurai to roam the "island" with Carnage, their leader, overlooking them.
The main piece was indeed Maximum Carnage, a haunted house featuring a nuclear reactor, and various villians, with Carnage taunting you the whole way. It was up to the visitor to escape.
Here's the main mystery: the haunted house allegedly featured grotesque images of dead and brutalized superheroes. Many sites cite a decapitated Spider-Man, Wolverine without his arms and Captain America covered in blood. However, despite the shocking and controversial nature of these, you can't find any pictures of these things.
The story goes that Marvel execs were furious over the portrayals, and subsequently refused to ever allow Marvel characters into HHH events again. Some speculate that the controversy was heightened due to the fact that the Spider-Man film starring Tobey Maguire had released earlier that year, and showing his decapitated corpse, even in a sort of "alternate universe", wasn't the best choice.
Unfortunately, besides a short promo video for Travel Channel and some grainy handheld camera footage that's barely visible (it's a dark haunted house), there is basically no footage of the haunted house of the event at Halloweem Horror Nights 2002.
Of course it makes sense - the internet wasn't even close to what it is now in 2002, and not everyone had a phone in their pocket that would pick up crystal clear footage of a dark haunted house. But still, one would logically think that the horrifying image of dead superheroes would be enough to generate even grainy images, or at least a few witness accounts. The mind begins to wander - did the dead heroes in the haunted house exist at all? There don't seem to be any news articles, or accounts or anything of this event. If it was really as controversal as it said, where is some evidence?
Personally, I think the landscape of tech was just too primitive to really get good images. If this had happened today, with both the advent of HD cameras on the average smartphone and the heightened popularity of Marvel characters due to recent blockbuster films, there'd be HUNDREDS of YouTube videos and images of this house and the area as a whole (There are also reports about trophies such as Iron Man's mask, Thor's hammer and Captain America's shield placed around the Island Under Siege).
If anyone else could shed some more light on this one, I'd love to hear it.