Anyone who’s Dungeon Mastered D&D 4th edition for even a little while should appreciate how easy it is to make a balanced encounter. Pick a target level, pick some monsters, add up their xp values, and make sure it’s within budget. It can get a little trickier if you don’t always know how many players will show up for the game (I balance my encounters for five, and write down what to add or subtract if I get the full 6 players, or only 4 for a given session.) But the basic equation is fairly simple.
Experienced GMs might want to consider playing around with the formula.
Here’s two examples:
First, a few weeks ago, I ran a fight between seven thirteenth level characters (!) and two dragons. I wanted it to be a big fight where the characters would have to use most of their dailies. As a result, I’d be looking at a target encounter level of 16. But I knew I wanted to do something different- present these dragons as cunning, ambushing creatures, and use terrain heavily.
The plan was that the dragons would have several pit traps around the first combat area- the Copper would stay close to the ground, and shift around, encouraging characters to come close to it, and the Blue would stay in the air, raining down lightning. Once a character fell down the pit, the Copper would follow, ravage the single character, and if bloodied or outnumbered, would fly through a trapped corridor, rigged to collapse, which it would trigger from the other side, to both do massive damage to the party members, and make it hard to navigate (one would have to Squeeze and crawl to get through after the rockfall stopped). Then there was a host of Gargoyle Harrier monsters on the other side (11th level lurkers), who would further fight the characters while the dragon(s) retreated to their inner sanctum.
So yeah, a huge battle, without any time to rest- if the party would try to take a short rest after dealing with the gargoyles, for example, the dragons would come charging out in full force. I had three full Paizo battlemaps ready for use. What actually happened, by the way, was that they forced the Copper down the hole themselves, then split up, taking the falling damage and going after it en masse, marking and putting conditions on it so it couldn’t easily make its escape, and finally pushed it to the ground, triggering the tunnel collapse on its corpse. Meanwhile the paladin used Knightly Intercession to pull the blue to the ground where they could put the whallop on it.
But here’s the total force in the encounter:
Custom Adult Blue Dragon (level 15 elite)
Custom Adult Copper Dragon (level 15 elite)
5x Sandy Pit Trap (level 15 lurker trap)
Cave in Tunnel (level 15 lurker trap)
6x Gargoyle Harriers (level 11 lurker)
By the rules, that’s 15000 xp worth of assorted baddies, or roughly an 18/19th level encounter for 7 characters. In practice, traps (pit traps especially) are overcosted, and the Harriers are not meant to be fought at the same time as the dragons. It’s still a nasty encounter, and would be nastier still if the players weren’t clever to finish it without having to face all the opposition.
Last week I ran an encounter featuring a chase through the city. There was a drake-pulled cart driven by an NPC, with the unconscious (player absent) Paladin, and several dragon eggs (rescued from said dragon encounter) in the back seat. I had several city map tiles placed in a winding fashion, so the cart would have to navigate them to get to a teleport circle. The fight started with 10 archer minions scattered on various rooftops over the map, an a Bearded Devil and several Legion Devils blocking their way. The cart would move a certain distance on its own, or player characters could take command of it to move it the way they wanted to. The reins of the cart changed hands several times during the encounter.
At the end of every round of the encounter, I rolled a single d6. On a 4-6, enemy reinforcements showed up, trying to stop the players from getting out of the city. Also, at the end, there were several enemies waiting for them.
The starting force included:
Bearded Devil (level 13 soldier)
4x Legion Devil Hellguard (level 11 minion)
1x Legion Devil Veteran (level 16 minion)
10x Jalalabad Archers (level 13 custom minion)
The ending force included:
Hulan the Glorious (a reskinned Drow Blademaster, level 13 elite skirmisher)
5x Jalalabad Dervishes (level 13 custom minion)
The Reinforcement rolls generated:
Jalalabad Outrider (level 13 custom skirmisher)
Human Gladiator (level 14 elite skirmisher)
5x Jalalabad Archers
Again, by the rules, that’s 7180xp worth of adversaries, or for 5 characters, a level 16 encounter. However, in practice, only a fraction of that value was attacking the characters at any given time, and the focus of the encounter was not on clearing the board of enemies. It was first on getting the cart and party to the destination, and then on getting away (there were two possible skill challenges to end the encounter- an Arcana based one to speed the teleport ritual, and a Social based one to talk down the enemy commander. Either one would end the encounter.)
The takeaway then, is when is using more creatures in an encounter a good decision?
*The party doesn’t fight all of them at once. For an encounter where there are waves of enemies, but they don’t all fight the characters at the same time, you can get away with having more enemies. This is probably the best way to do a traditional dungeon map with lots of tiny rooms and a monster in each one. As the party fights one monster, they draw the attention of more, and more and more of the map gets used as the encounter goes on. Maybe the whole dungeon level is a single encounter!
*Some condition vastly overvalues the xp value of the monsters. I’m of the opinion that pit traps are undervalued compared to a monster of the same level- they get one attack, then they are pretty much out of the fight unless forced movement is in play, but that’s something that generally the players have more access to than the GM unless the encounter is specifically built towards that. But any monster can be overvalued; suppose you’ve got a party full of fire-using characters. With Fire being the most common resistance in the game, you might turn that on its head and let them fight a host of Fire-Vulnerable creatures- such as Chillborn zombies. For a level 6 party with multiple fire-heavy characters, 8 Chillborn Zombies (technically a level 9 fight) is likely to be much easier than it looks- a great way for those fire users to show off and feel vindicated!
*There’s something at stake other than killing or being killed. In the second example, the party was just trying to get away. You could turn that on its head and have an escaping villain with waves and waves of minions between him and the party. Can they cut their way through the wave to put the conditions on him they need to stop his escape? (Probably. Player characters seem to be really good at that sort of thing. Make them work for it!)
*There’s an alternate victory condition. The second example has a skill challenge to end the fight. A fight that ends when a single badass leader is slain (especially if the players can figure this out, perhaps with an Insight or other skill check) can be much easier if the players focus their fire on that sole badass leader. Or maybe there’s a switch for a castle gate that let’s the King’s cavalry storm in- but an advance force of awesome adventurers is needed to get past all the evil wizard’s men that are between them and it, creating an environmental challenge. (Put lots of things to climb onto and jump from, and multiple paths to get there, and you’ll have a recipe for an encounter based on movement and getting to a key location, not just clearing out the other guys.)