Bodycount

Watched the truly awful film, ‘The Tournament’ last night. Not much to recommend about it (Robert Carlyle is utterly wasted and the parkour guy spends an amusing amount of time around on the rooftops), but it did give me an idea for a scenario.
Bodycount Fantasy Scenario
The city of High Redoubt was once the southern shield of a mighty kingdom. High, impregnable walls encircle the town and easily withstood sieges from rival kingdoms, rebellious Barons and Barbarian Hordes. Never once in its martial history had the town ever been taken.

But that was many years ago. The old kingdom fell and High Redoubt became an independent city-state of sorts, ruled by the relatively benevolent Blackard Barony. Supported by the surrounding valley full of prosperous farms and rich mines, but no longer strategically important and located just far away enough from the main roads, the city has been at peace for almost two hundred years.

Those qualities; peaceful, remote and encircled by heavy walls are what made it the perfect location for the Order of Chaos’ most nefarious entertainment.

At sundown of the day the party is spending a quite evening High Redoubt, the gates of the city are inexplicably and magically locked from the outside. Almost immediately fifty of the most infamous, insane and psychotic members of the Order reveal themselves and begin murdering each other, and the townsfolk. The last member of the Order standing at sunup is awarded the Mask of Yob-Slobbersloth and a seat on the Order’s ruling council.

There are no rules; thieves and assassins strike from the shadows. Warriors battle it out in the courtyards and taverns while sorcerers and wizards cast powerful spells, obliterating entire buildings and summoning horrors to hunt in the streets.

Can the party survive until morning?

Modern Scenario
I won’t ruin the film. If you're keen, watch the movie (available on Netflix)

Sci-Fi Scenario
Same as above, but easily set on a remote asteroid colony.