1) A bad reputation can be troublesome- Normal people are going to avoid them like the plague- so noone to buy or sell items, give them lodging, heal them etc...
2) If the area is civilized, bar the town gates! Do not allow them into settlements under orders of the local magistrate. If they attempt to break in the gates, have the town guard resist with the aid of several adventuring NPCs within the town.
3) If they are of higher level, the local authority may declare them enemies of the state and hire adventurers to arrest them. These adventurers should be a real threat to the party, but will attempt to capture them alive, so they can be stripped of all their possessions and rot in a suitable prison (until you the DM see fit to allow them out)
Hopefully they will get the hint and modify their character's behavior so it is not psychopathically evil and harmful to your game. If it doesn't, then you need the deus ex machina option- something out of nowhere that mops the floor with them. Mine was a Fighter 10/Blackguard 20 Death Knight that decided a particular party member had surpassed his reputation for evil and was going to make an example of him. The fight didn't last long, and the character (and player) never caused trouble again.
They have been getting very detail oriented on the small stuff and killing everyone that stands in front of them (even NG aligned NPC's). I haven't seen them act this way in previous games, so it was very unexpected (and quite annoying). I need advice on how to reign them in while still allowing them some measure of freedom.
Hmmm... I am not sure what you mean by "getting very detail oriented". If these players are more experienced than you as a DM and it is causing problems there are a couple of solutions:
1) Talk to your players. Explain why you ain't having fun because they are effectively sabotaging the game. They should be able to understand that. If they want to play evil characters and go on a killing rampage, decide for yourself if that is the kind of game YOU want to DM. If not, find other players or become a player yourself.
2) Use their tactics against them. This is quite reasonable. If the party promotes a particular tactic that always works of course others are going to hear about it and learn from it.
3) Read forums like the one called "What is a DM to do?" or some such. There you should be able to get plenty of non-world specific advice on how to "beat" your experienced players using the same rules as they use (it is no problem beating players when you have powerful monster to add to the game, but it is somewhat more "fair" to beat them by simply using the smart combinations the rules allows for).
4) If them killing Neutral good characters is a problem for you, think about what would happen in your world if someone behaved like that? First, the cops would drop by. Kill them, more cops show up. Eventually you'll be paid a visit by the SWAT team and if you manage to kill them perhaps some counter-terrorist force. After that, you'll probably be recruited into a vicious sub-unit of the intelligence community :D Have you NPC's react accordingly. Keep bringing in more powerful NPC's to teach them a lesson or eventually negotiate a stop to their murderous behavior.
:-) Jesper
I don't want them to die, but I think I've been way too easy on them so far.
...killing rival church members who were attempting to negotiate, but weren't given a chance.
Sounds like they supplied the rival church with some martyrs. Perhaps this could be used against them!
As for other Mystaran baddies, I'll have to think about that some...
Once arrested, role-play their trial, listing the evil deeds that the authorities know about and can prove (preferably through witnesses and survivors detailing the Pc depravity and how it affected them). If the PCs attempt to escape, Roll-play the escape (IE, turn it into Hack and Slash, emphasis on Slash). If they don't, let them serve their time (time passes for 20-30 years while they rot in jail and are let out on good behavior). Hopefully the characters are wiser, older and a little more good. Try your best not to make it a death sentence unless you want them to attempt an escape (the survivors ask for leniency, etc).
Or...
In your next Campaign you can have these PCs as evil characters that your players must defeat (I rarely allow an evil party, and when they turn evil without any reform, I turn them into NPCs and ask the players to roll new characters).
Then have an NPC cousin/brother etc of a victim just "happen" to be a member of the local thieves guild.
Next time they stay in a tavern, their rooms get raided and any cash/jewels/magic items get lifted by the thieves as payback (maybe a sympathetic magic user casts a sleep spell to help things along), leaving them with just the basics.
THEN have the local tax inspector turn up (with some burly assistants) and throw them in the pokey for non-payment of taxes. :D
Other than Dragons and possibly Bargle The Infamous, are there any Mystara specific "big baddies" and/or particularly perilous locations or modules?
*************** Possible spoiler for players in Karameikos!! ***********
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Well, there are a number of interesting vampires and nosferatu i Karameikos, particularly Lord Sulescu, who is going to be greatly offended by boisterous PC's harming "his people" (i.e. his village and the surrounding lands).
Other than that, there is any number of big bad wizards in Glantri and Alphatia, who could be offended (perhaps without the PC's even knowing it :D )
Major churches such as the Church of Karameikos is also a good idea.
And lastly, one of my favourites: giants. They have had a major power boost from 2nd edition to 3E and should make short work of most parties of adventurers below 10th level.
:-) Jesper
Once arrested, role-play their trial, listing the evil deeds that the authorities know about and can prove (preferably through witnesses and survivors detailing the Pc depravity and how it affected them). If the PCs attempt to escape, Roll-play the escape (IE, turn it into Hack and Slash, emphasis on Slash). If they don't, let them serve their time (time passes for 20-30 years while they rot in jail and are let out on good behavior). Hopefully the characters are wiser, older and a little more good. Try your best not to make it a death sentence unless you want them to attempt an escape (the survivors ask for leniency, etc).
You can make it more complex by having the PCs be deported to some forlorn location (or sold into slavery/indentured servitude). Suitable places can be the Thyatian Hinterlands, the prison islands run by Thyatis and Ierendi (prison deep in the jungle!), or the Savage Coast (the perfect place to drop undesirable people who can't be held otherwise, since the red curse tend to keep people within the Haze).
If the party is higher level, the prison can be some place that is even more difficult to escape (another dimension).
An IMO interesting variant is to have the (mid to high level) PC sent to a ``special'' prison built to hold people like them. You can find a lot of inspiration from movies (Alien's prison planet), comics (the rieducation center in Kingdom Come, Sentinel's prison island in some X-Men story), or books (I'm thinking of a short-story, ``Sepultura'', by Valerio Evangelisti, set in a prison where inmates are held in a sort of protoplasm that prevents them from moving)
One thing I have found useful is to introduce some NPCs as friends of the PCs. Bring in their families, childhood friends etc. And if they do something studpid, make them see how this makes these NPCs suffer. If they fail to negotiate peace between the Churches, perhaps one PCs baby sister gets sick and needs a rival Cleric to heal her. He will refuse ofcourse, and killing him is not going to help the sister.
Finally, don't award XP for killing! This is the dumbest idea D&D ever came up with. Reward XP for completing quests, good roleplaying, interracting with NPCs, coming up with unexpected things, falling in love, getting into politics, making a crazy speech, doing something stupid in a cool way, rescuing a wonded sheep/fair maiden/old man from the wolf/orcs/dragon/tax collector. Not for killing! Definately not for killing NPCs who aren't hostile to begin with.
Håvard
Then I would send knights from the Order of the Griffon to arrest them under orders of the Church of Karameikos and King Stephan. Until they are captured, prevent them from finding refuge in towns and settlements- word of their crimes should have gotten around, and anyone not strong enough to stop them is going avoid them....
The ones killed were Church of Halav Incarnate (Cult of Halav) members, so some were at least chaotic if not evil, but some were good. Two of them got away, so you can bet reputations will be spreading. As for the Order of the Griffin, they are currently camped outside the temple entrance waiting for the party to come out (and are "protecting" the party's 2 goblin auxiliaries, 8 horses and cart). They know nothing yet of the murders. The party knows they are outside and are are stalling, exploring every corner for another way out, and talking of the best way to kill the Griffins. 2 out of 7 players have a problem with this (monk and cleric), but I don't know if they can convince the rest otherwise.
I had already decided to grant additional XP to those not involved in the killing, and more still to the monk and cleric if they can calm the rest down. I have always considered roleplaying awards a good idea.