While a Dungeon Master knows that they shouldn’t set up overly imbalanced scenarios designed only for the purpose of murdering the party, many DMs go to the opposite direction and make their encounters too easy, which is just as much of an abuse to players as Killer DMing is. It isn’t that they intend to create them that way, typically they are following the rules, but what they aren’t doing is running the monsters to their full potential.

The DM is expected to be an impassive witness to the game; unfortunately, when a DM doesn’t understand that he is also expected to actually role-play his monsters, then he isn’t bringing his best to the table, nor the best out of his players. Some DMs assume that players are running through encounters because they are so good at it, and choose to over-compensate by throwing more power monsters at the players, which they don’t role-play either.

Your intent while running the encounter should be to keep your monsters alive and to kill all of the players while still following the rules. We aren’t telling stories, we are running an encounter, and if we do a good job running it, then the players will see a story in it. We want to make each and every encounter as dangerous as we possibly can with the tools that we have. This applies for both Module adventures as well as the encounters which we create ourselves. If we stick to the rules of creating balanced encounters, we can really bring a lot of danger to each one.

ROLE-PLAYING MONSTERS EFFECTIVELY

Intelligence is clearly listed in the Monstrous Manual, and we need to observe it. Naturally a 0 INT character is going to be a machine: A zombie does not care if it is going to get hurt, an Iron Golem is going to work only as it was designed to, and a deadly pudding is going to satisfy its hunger. 0 INT creatures will never stop until they are dead.  

Creatures with INT of 1-2 are animals. If they are untrained, they may or may not try to run away once they realize that their lives are in danger. We can run this randomly by applying Morale checks every round. Animals should act like animals.

Creatures with normal Intelligence are far more dangerous then you might be giving them credit for. They won’t just feed themselves to a meat grinder, they need to be role-played and they should hatch plots and value things that they enjoy.  Thinking of motivations for them should be fun for the DM, though it would be a waste of time to figure out specific motivations for each and every creature living in a lair, we can assign a group motivation and have one or two that have alternative motives, typically having something to do with personal ambitions.

The boss of an area should be more thought out; he is the most dangerous thing in the lair because of his mind. He is leading a small army, and he should have a personal goal assigned to him, in particularly keeping his army alive and his personal power intact.

KEY IS THE KEY

Many modules tell the DM what the monsters are doing, this in no way implies that they won’t investigate noises unless the key specifically says that they won't. The key takes for granted that the party isn’t standing around arguing about which direction to go, or who has the right to take the magical item, and all of the other stuff that players like to complain about. Once the alarm is tripped, things shouldn’t go so good for the players; all of those monsters should be free to start roaming the dungeon.

You and your monsters need a solid plan. Prior to play you should really study your map, and pick out good ambush spots where you can surround the players, or sneak up behind them. Once an intruder is detected, word should spread around really fast, and all monsters should report to their battle stations.. A patrol will be sent out to locate the invaders, and try to identify the nature of the party; instead of attacking, they’ll do their best to report this information to their allies.

MONSTER TACTICS

The MM holds clues about tactics of each monster, but it is up to the DM to really bring them to life and keep them as safe as possible. Survival is key! The lower the monsters HD, the less likely they’ll engage in direct combat. Instead, they’ll prefer ranged combat and the use of traps, only entering direct combat if they have no other options. These are complex creatures and the encounters with them starts with the planning stage. They will use their lairs to their advantage, setting up traps that they’ll trigger themselves, else know how to avoid. What they won’t do is all go rushing out of their lair to defend it. The lair itself is their preferred weapon and it is defensively superior to any melee weapons that they have.

Same goes for wilderness encounters; they will set up traps and do their best to catch their intended victims, namely merchants. If a caravan looks too dangerous they’ll probably let it go unless they are really in need of supplies, then they will become braver, and this is when they are most likely to encounter PCs. They should have plans set in place to favor them, and keep them from having to engage in direct combat. This should also include a great escape route, because lets face it, bravery and overt boldness are two different things.

MONSTERS AND THEIR TREASURE

DMs like to hide treasure around their dungeons, but if a monster is aware of it, and knows how to use it, he most certainly will, and it might not just be the head boss that has the treasure, if you were an underling with ambition for better things, would you tell your boss that you have found a Ring of Protection, or a Sword+3? If you are into telling stories, this is where you should hide it. Is the party even going to notice the ring on a dead gnoll’s finger? What would his peers think about the gnoll not knowing his secret? Maybe a couple of them do know and have been looking for an opportunity to take it from him? This is role-playing! And while it won’t stop the players from beating you, it will slow them down and they won’t get anything for free, which will make the encounter more special to them in the long run.