Once you've built a monster with a few class levels to challenge player characters, you still must rate the challenge. Unfortunately, that task is a little more complicated than it seems at first. Fortunately, the rules provide plenty of material to guide you through the task.
You can find guidelines for matching foes to player characters on pages 37-38 and 48-50 in the Dungeon Master's Guide and pages 293-294 in the Monster Manual.
Challenge Rating (CR)
As noted in Part One, a creature's Challenge Rating is a general measure of how much danger the creature poses during an encounter. A creature's CR indicates the average level that a party of four fresh characters would find moderately difficult to defeat; see page 7 in the Monster Manual for details.
From page 7 of the Monster Manual:
This shows the average level of a party of adventurers for which one creature would make an encounter of moderate difficulty. Assume a party of four fresh characters (full hit points, full spells, and equipment appropriate to their levels). Given reasonable luck, the party should be able to win the encounter with some damage but no casualties. For more information about Challenge Ratings, see pages 36 and 48 of the Dungeon Master's Guide.
It's important to remember that CR measures a creature's ability to challenge a party of four characters during a single encounter. A creature's Challenge Rating is no indication of how formidable it could prove as a player character. A monster that PCs meet during an adventure is present for one or two encounters at most. A player character, on the other hand, is present for just about every encounter in the campaign -- that is why the game includes level adjustments. A creature's CR and its character level or ECL can be wildly different, and that's a good thing because CR and character level or ECL measure different things.
CR Adjustments for Class Levels
Usually, it's pretty simple to calculate the CR for a creature with a few class levels -- just add the creature's class levels to its base CR (that is, the CR the creature has when it has no class levels at all). You need to be alert, however, for variations on the basic rule.
Creatures with NPC Class Levels: When a creature has levels in one of the NPC classes presented in Chapter 4 in the Dungeon Master's Guide, subtract one from the class level before adding it to the base CR. A creature's CR, however, always increases by at least +1 when it has an NPC class level.
From page 38 of the Dungeon Master's Guide:
Since NPC classes (see Chapter 5: Campaigns) are weaker than PC classes, levels in an NPC class contribute less to a creature's CR than levels in a PC class. For an NPC with an NPC class, determine her Challenge Rating as if she had a PC class with one less level. For a creature with monster levels in addition to NPC class levels, add the NPC levels -1 to the creature's base CR (always adding at least 1).
Humanoids with No CR or Racial Hit Dice: Humans and other standard races from the Player's Handbook have no Hit Dice or CR except for what they gain from their class levels. Such creatures have a CR equal to their class levels. If the creature has levels from an NPC class, subtract one from the number of NPC levels they have when calculating CR. If the creature has only one NPC class level, it has a CR of 1/2.
See pages 37-38 in the Dungeon Master's Guide for an extended example of this rule in action.
Creatures with Nonassociated Class Levels: Sometimes, adding class levels to a creature doesn't make it more dangerous to foes. When that happens, not all the level are added to the creature's basic CR.
Only levels equal to or less than the creature's racial Hit Dice can be nonassociated. Divide any nonassociated class levels in half before adding to the base CR to get the increased CR for the class levels.
The rules don't say so, but you should round down if the number of levels isn't an even number. If you're adding NPC class levels, subtract one before dividing (and you still round down).
Here's an example of a CR adjustment using nonassociated class levels: A troll has 6 racial Hit Dice and a CR of 5. If a troll has six levels in a nonassociated class from the Player's Handbook, the troll has a CR of 8 (1/2 of 6 is 3 + 5 = 8). If the same troll, however, adds one more level in the same class, the troll's CR is 9.
The rules don't provide much in the way of guidelines for deciding when a class should be nonassociated, so it's always a judgment call for the DM.
In general, a class should be nonassociated when its characteristics don't mesh well with the creature's own abilities. For example, a fire giant is basically a fighting creature. Adding a level in a class that doesn't do much to improve that fighting ability, such as sorcerer or wizard, probably won't make it much more formidable in battle. I say "probably" because it's possible to make just about any class mesh well with a creature's racial prowess.
Suppose a tribe of fire giants includes a sorcerer who knows a collection of workaday spells such as mending, alarm, and locate object. The fire giant sorcerer mostly helps the chief keep the others in line and performs small magical services for the rest of the tribe as needed. The example fire giant probably will rely on its fighting ability in combat and its sorcerer levels won't have much effect in a battle. This creature is a prime candidate for nonassociated class levels.
Now let's suppose we have a particularly clever fire giant sorcerer whose spell list has been carefully tuned for combat. This fire giant knows spells such as shield, true strike, blur, and haste. This fire giant could become a real juggernaut in combat, and all its sorcerer levels should increase its CR.
Encounter Level (EL)
Once you've found the correct CR for all the creatures with class levels in an encounter, you determine the encounter's EL in exactly the same way you'd determine the EL in any other encounter. Table 3-1 in the Dungeon Master's Guide is your primary tool for determining Encounter Levels.
Table 3-1 works well for groups of creatures with the same CR, but doesn't work so well for groups of creatures with varying CRs. Here are a few tips and reminders for dealing with such groups:
- When two creatures have the same CR, the EL for an encounter featuring them is two higher than the shared CR. For example, two CR 9 creatures make an EL 11 encounter. (But be sure to check Table 3-1: Encounter Numbers for those low-CR creatures.)
- When two creatures have CRs within two points of each other, the EL for an encounter featuring them is one higher than the highest CR. For example, a CR 9 and CR 8 creature make an EL 10 encounter. A CR 9 and CR 7 creature also make an EL 10 encounter.
- When two creatures have CRs that differ by three or more, use the higher CR to determine the encounter's EL. For example, a CR 9 and CR 6 creature make an EL 9 encounter.
- When you have a large number of creatures with different CRs, you can determine the EL for an encounter by arranging them into groups of similar CRs and then grouping the results. Here's an example: A group of creatures contains eight monsters of CR 3, three monsters of CR 7, and a leader with CR 10.
According to Table 3-1, eight CR 3 monsters have an EL of 9.
Two CR 7 monsters also have an EL of 9.
Combining the two ELs of 9 produces an EL of 11.
An EL 11 group combined with the CR 10 leader produces an EL of 12 for the whole encounter.
That wraps up our discussion of various levels. Hopefully you're now more prepared to create monstrous player characters and monsters with class levels as foes for player characters.
About the Author
Skip Williams keeps busy with freelance projects for several different game companies and was the Sage of Dragon Magazine for many years. Skip is a co-designer of the D&D 3rd Edition game and the chief architect of the Monster Manual. When not devising swift and cruel deaths for player characters, Skip putters in his kitchen or garden (rabbits and deer are not Skip's friends) or works on repairing and improving the century-old farmhouse that he shares with his wife, Penny, and a growing menagerie of pets.