Zendragon said:
I am making a timed module. There are lots of demons involved and are scattered around a castle, both inside and atop the castle. Due to a curse, these demons can't leave the castle area. I have a rotating guard shift, but nothing else. So the question is what do demons do in their off time? There are no primes to torture and no end in site for the curse to be lifted.
When you say 'demon' I assume you mean Tanar'ri or any other chaotic evil outsider native of the Abyss. If you just mean 'fiend' in general, you'll have -vastly- different reactions from Baatezu, Yugoloths, Gehreleths/Demodands, Rakshasa, etc. My answers pertain to Tanar'ri and other Abyssal denizens only:
What is binding them to the site, and are they summoned or actually there physically (like if they had gated, planeshifted, or used a portal)? Given their nature, being confined and controlled even in a slight way would drive them nuts (not that many could tell the difference). If killing themselves was an option to escape being thus bound, they'd slaughter one another with glee, and then kill themselves.
If the binding would prevent that sort of easy way out, they'd act to amuse their own whimsy, but in as unorganized a fashion as possible. If they could summon more of their kind, they would, even if only to have something to fight or f*ck. Those last two things are probably at the top of the list of fun things to do while bound to a location on the prime material plane.
They'd first slaughter everything that wasn't also Tanar'ri, then they'd go about redecorating their surroundings (which would be somewhere between destroying it, piece by piece, and making legitimate but horrible and bizarre changes to the place), then they'd probably split their time between screwing themselves and each other, and torturing or killing one another. The only thing to take them away from this general scheme would be anything mortal wandering into range that they might use first to escape being bound to the place, and if that wasn't possible, they'd screw/torture/kill the mortal.
The above mentioned ideas will vary depending on any specific subtypes of Tanar'ri, or non Tanar'ri chaotic evil fiends, involved. A glabrezu will react differently to this than a bunch of Vrocks, and a group of Bebeliths will react differently than any Tanar'ri, etc.