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Encounter Design in 4th Edition

Design & Development

by Mike Mearls

The Design & Development article series premiered on the D&D website back in September 2005, and has been a staple ever since. With the approach of 4th Edition, and our designers and developers focused on the new edition, this column will be the primary vehicle for 4th Edition coverage. We’ll not only give you peeks at what’s forthcoming, but also the “how” and “why.”
Keep in mind that the game is still in a state of flux, as refinements are made by our design and development staff. You’re getting a look behind the curtain at game design in progress, so enjoy, and feel free to send your comments to

The encounter serves as the basic building block of a D&D adventure. In the old days, DMs used their experience, judgment, and sense of drama to build encounters. The 3rd Edition of D&D gave us challenge ratings and encounter levels. They were great tools, but they assumed that the party fought only one monster. In 4th Edition, we’re doing things a bit different. We’re shifting to a system that assumes a number of monsters equal to the number of characters. This change has a few major implications for encounter design:
  1. Superior Accuracy: Before we can talk about encounter design, it’s important to note that while 3rd Edition’s CR system is a useful measuring tool, it isn’t always an accurate one. A monster’s AC, hit points, special attacks, and damage all combine to determine its level. In the old days, we relied on a designer’s best guess to match a creature to a CR. While designating a creature’s level is still an art, designating a creature’s level now has more science behind it. By creating robust progressions of attack bonus, damage, and AC, level has become a much more accurate measure of a monster’s power. This step is critically important, as it now allows us a lot more accuracy in determining the threat an encounter presents.
  2. More Monsters: Rather than pick one monster, you now select a group of critters. The interplay between monsters is a little more important in design. In 3rd Edition, you had to turn to significantly weaker monsters to put a pair or more creatures into a fight. Unless these monsters had significant advantages when working together, an individual character easily outclassed an individual monster in such a group. In 4th Edition, an individual creature (of a level comparable to the PC) has the AC, attack bonus, and hit points to remain a threat during a fight.
  3. Monster Roles: Monsters have roles that define the basics of how they fight. The role functions in only the broadest terms. It dictates a few basic measures of a monster but describes, rather than proscribes, how its abilities work. The real strength of a role is that it gives designers a few basic targets to shoot at it in design, ensuring that every monster we make fits in with the rest of the creatures in the whole game. For instance, monsters that are good at ranged attacks love to have a beefy wall of brutes in front of them to hold back the adventurers. Roles allow you to focus in on the right monster for the encounter and spot obvious combinations.
  4. Hazards: Traps, hazards, dangerous terrain, and other complications have a clearer place in the battlefield. The 3rd Edition of D&D gave us one “monster unit” to play with. In other words, the game assumed that the encounter consisted of four PCs against one monster. If you had five PCs, you had to figure out how to get 1.25 “monsters” into the encounter. Even worse, that system had to express traps, hazards, and other dangers as full monster units. It was difficult at best to mechanically represent something that was never meant to stand alone.

    In 4th Edition, each monster represents only a portion of the encounter. That makes it much easier to design green slime, pit traps, whirling blades, fountains that spray acid, and crumbling stone walls. One such hazard can simply take the place of one monster, leaving you with three or four monsters in the encounter. Since monster level is a more rigorous measure of power, we can turn those measures and scales around and use them to create environmental hazards, traps, set pieces, and other interesting tactical twists.

Putting it All Together

What does all this mean for encounter design in 4th Edition? When you build an encounter, you can begin from several different premises. You can start with a cool monster, find creatures that make good “teammates” for it, and run with that. For instance, you’ve always wanted to throw a medusa at the party. Looking at her stats, abilities, and role, you can then pick out other creatures that make her a tougher nut to crack. Of course, you could always throw a couple medusas at the characters and have a little sculpture party.
Alternatively, you can start with a basic idea of how you want the encounter to proceed, pick out monsters based on level and role, and throw that at the party. Let’s say that the party wizard hasn’t had sufficient trouble thrown his way recently. Ranged attackers always make life difficult for spellslingers, so you can pick out a few of them based on role. To keep the fight busy, a monster with a lot of abilities to hinder and slow down PCs fits the bill. As a cherry on top of this anti-wizard sundae, you can finish the encounter with a lurker who hides from the party, sneaks past the fighter, and springs from the shadows to chop down the caster. The key here is that, without knowing exactly which monsters to use, you have an idea of which types of critters you want.
How you fit hazards into an encounter is perhaps the most important aspect of encounter design in 4th Edition, and it brings us to the third way you can build encounters. You can now more easily add dynamic elements to an encounter and account for cool special effects, hazards, and traps. Those elements are, in mechanics terms, equal to a monster. They fit seamlessly into the encounter design and XP rules by taking up one creature’s slot. If you want to throw in more hazards, simply reduce the monster count and increase the number of hazards present in the encounter.
If you’re like me, and you read too many comics and watch too many movies for your own good, you like to pull out set pieces and crazy terrain to throw at the party. A swaying rope bridge battered by howling air elementals fits under the encounter building system. A burning building that collapses around the PCs as they fight the evil hobgoblin wizard fills a similar role, as does a bizarre altar to Vecna that randomly teleports characters around the room. Hazards, traps, and other dangers simply fill in for one or more creatures in a fight.
By expanding the tools and making them work well together, 4th Edition presents a more robust, flexible, extensible, and exciting set of encounter tools. If the 3rd Edition’s presentation of CR was the first step to taking some of the mystery out of encounter design, the 4th Edition builds on that core to produce a more accurate tool, along with additional uses for that tool.

About the Author
Mike Mearls is found only in subterranean places, as he detests sunlight. He is greatly evil and considers the bulk of humanity (and its kin) as cattle to feed upon. He speaks only his own arcane language and several other weird tongues -- purportedly those of terrible races of things which dwell in regions of the subterranean world far deeper than mankind has ever ventured.


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