As a very general rule of thumb, each level = about 1/2 CR. So a CR 1 creature with 10 levels of sorcerer would add up to a CR 6 creature. This is the method I use when considering monsters with class level during idle brainstorming, and it gives you an impression of what the finished product will look like once you've made it. Improving Monsters. Each of the monster entries describes a typical creature of its kind. However, there are several methods by which extraordinary or unique monsters can be created using a typical creature as the foundation: by adding character classes, increasing a monster’s Hit Dice, or by adding a template to a monster. These methods are not mutually exclusive—it’s possible for a.
Each of the monster entries describes a typical creature of its kind. However, there are several methods by which extraordinary or unique monsters can be created using a typical creature as the foundation: by adding character classes, increasing a monster’s Hit Dice, or by adding a template to a monster. These methods are not mutually exclusive—it’s possible for a monster with a template to be improved by both increasing its Hit Dice and adding character class levels.
Class Levels
Intelligent creatures that are reasonably humanoid in shape most commonly advance by adding class levels. Creatures that fall into this category have an entry of 'By character class' in their Advancement line. When a monster adds a class level, that level usually represents an increase in experience and learned skills and capabilities.
Increased Hit Dice
Intelligent creatures that are not humanoid in shape, and nonintelligent monsters, can advance by increasing their Hit Dice. Creatures with increased Hit Dice are usually superior specimens of their race, bigger and more powerful than their run-of-the-mill fellows.
Templates
Both intelligent and nonintelligent creatures with an unusual heritage or an inflicted change in their essential nature may be modified with a template. Templates usually result in tougher monsters with capabilities that differ from those of their common kin.
Each of these three methods for improving monsters is discussed in more detail below.
Ability Score Arrays
Monsters are assumed to have completely average (or standard) ability scores—a 10 or an 11 in each ability, as modified by their racial bonuses. However, improved monsters are individuals and often have better than normal ability scores, and usually make use of either the elite array or the nonelite array of ability scores. Monsters who improve by adding a template, and monsters who improve by increasing their Hit Dice, may use any of the three arrays (standard, nonelite, or elite). Any monster unique enough to be improved could easily be considered elite.
Elite Array
The elite array is: 15, 14, 13, 12, 10, 8. While the monster has one weakness compared to a typical member of its race, it is significantly better overall. The elite array is most appropriate for monsters who add levels in a player character class.
Nonelite Array
The nonelite array is: 13, 12, 11, 10, 9, 8. The nonelite array does not necessarily make a monster better than normal, but it does customize the monster as an individual with strengths and weaknesses compared to a typical member of its race. The nonelite array is most appropriate for monsters who add class levels in a NPC class.
Ability Score Improvement
Treat monster Hit Dice the same as character level for determining ability score increases. This only applies to Hit Dice increases, monsters do not gain ability score increases for levels they 'already reached' with their racial Hit Dice, since these adjustments are included in their basic ability scores.
Monsters And Class Levels
If a creature acquires a character class, it follows the rules for multiclass characters.
The creature’s Hit Dice equal the number of class levels it has plus its racial Hit Dice. A creature’s 'monster class' is always a favored class, and the creature never takes XP penalties for having it. Additional Hit Dice gained from taking levels in a character class never affect a creature’s size.
Humanoids and Class Levels
Creatures with 1 or less HD replace their monster levels with their character levels. The monster loses the attack bonus, saving throw bonuses, skills, and feats granted by its 1 monster HD and gains the attack bonus, save bonuses, skills, feats, and other class abilities of a 1st-level character of the appropriate class.
Level Adjustment and Effective Character Level
To determine the effective character level (ECL) of a monster character, add its level adjustment to its racial Hit Dice and character class levels. The monster is considered to have experience points equal to the minimum needed to be a character of its ECL.
If you choose to equip a monster with gear, use its ECL as its character level for purposes of determining how much equipment it can purchase. Generally, only monsters with an Advancement entry of 'By character class' receive NPC gear; other creatures adding character levels should be treated as monsters of the appropriate CR and assigned treasure, not equipment.
Feat Acquisition and Ability Score Increases
A monster’s total Hit Dice, not its ECL, govern its acquisition of feats and ability score increases.
See also: Monsters as Races
Increasing Hit Dice
As its Hit Dice increase, a creature’s attack bonuses and saving throw modifiers might improve. It gains more feats and skills, depending on its type, as shown on Table: Creature Improvement by Type.
Note that if a creature acquires a character class, it improves according to its class, not its type.
| Type1 | Hit Die | Attack Bonus | Good Saving Throws | Skill Points2 |
|---|---|---|---|---|
|
||||
| Aberration | d8 | HD ×¾ (as cleric) | Will | 2 + Int mod per HD |
| Animal | d8 | HD ×¾ (as cleric) | Fort, Ref (and sometimes Will) | 2 + Int mod per HD |
| Construct | d10 | HD ×¾ (as cleric) | — | 2 + Int mod per HD3 |
| Dragon | d12 | HD (as fighter) | Fort, Ref, Will | 6 + Int mod per HD |
| Elemental | d8 | HD ×¾ (as cleric) | Ref (Air, Fire), or Fort (Earth, Water) | 2 + Int mod per HD |
| Fey | d6 | HD ×½ (as wizard) | Ref, Will | 6 + Int mod per HD |
| Giant | d8 | HD ×¾ (as cleric) | Fort | 2 + Int mod per HD |
| Humanoid | d8 | HD ×¾ (as cleric) | Varies (any one) | 2 + Int mod per HD |
| Magical beast | d10 | HD (as fighter) | Fort, Ref | 2 + Int mod per HD |
| Monstrous humanoid | d8 | HD (as fighter) | Ref, Will | 2 + Int mod per HD |
| Ooze | d10 | HD ×¾ (as cleric) | — | 2 + Int mod per HD3 |
| Outsider | d8 | HD (as fighter) | Fort, Ref, Will | 8 + Int mod per HD |
| Plant | d8 | HD ×¾ (as cleric) | Fort | 2 + Int mod per HD3 |
| Undead | d12 | HD ×½ (as wizard) | Will | 4 + Int mod per HD3 |
| Vermin | d8 | HD ×¾ (as cleric) | Fort | 2 + Int mod per HD3 |
Size Increases
A creature may become larger when its Hit Dice are increased (the new size is noted parenthetically in the monster’s Advancement entry).
A size increase affects any special ability the creature has that is affected by size. Increased size also affects a creature’s ability scores, AC, attack bonuses, and damage values as indicated on the tables below.
| Old Size1 | New Size | Str | Dex | Con | Natural Armor | AC/Attack |
|---|---|---|---|---|---|---|
|
||||||
| Fine | Diminutive | Same | -2 | Same | Same | -4 |
| Diminutive | Tiny | +2 | -2 | Same | Same | -2 |
| Tiny | Small | +4 | -2 | Same | Same | -1 |
| Small | Medium | +4 | -2 | +2 | Same | -1 |
| Medium | Large | +8 | -2 | +4 | +2 | -1 |
| Large | Huge | +8 | -2 | +4 | +3 | -1 |
| Huge | Gargantuan | +8 | Same | +4 | +4 | -2 |
| Gargantuan | Colossal | +8 | Same | +4 | +5 | -4 |
| Old Damage (Each)1 | New Damage | |||||
|---|---|---|---|---|---|---|
|
||||||
| 1d2 | 1d3 | |||||
| 1d3 | 1d4 | |||||
| 1d4 | 1d6 | |||||
| 1d6 | 1d8 | |||||
| 1d8 | 2d6 | |||||
| 1d10 | 2d8 | |||||
| 2d6 | 3d6 | |||||
| 2d8 | 3d8 | |||||
Templates
Certain creatures are created by adding a template to an existing creature. A templated creature can represent a freak of nature, the individual creation of a single experimenter, or the first generation of offspring from parents of different species.
Acquired And Inherited Templates
Some templates can be added to creatures anytime. Templates such as these are referred to as acquired templates, indicating that the creature did not always have the attributes of the template.
Other templates, known as inherited templates, are part of a creature from the beginning of its existence. Creatures are born with these templates.
It’s possible for a certain kind of template to be of either type.
Reading A Template
A template’s description provides a set of instructions for altering an existing creature, known as the base creature. The changes that a template might cause to each line of a creature’s statistics block are discussed below. Generally, if a template does not cause a change to a certain statistic, that entry is missing from the template description. For clarity, the entry for a statistic or attribute that is not changed is sometimes given as 'Same as the base creature.'
Size and Type
Templates often change a creature’s type, and may change the creature’s size.
If a template changes the base creature’s type, the creature also acquires the augmented subtype unless the template description indicates otherwise. The augmented subtype is always paired with the creature’s original type. Unless a template indicates otherwise, the new creature has the traits of the new type but the features of the original type.
If a template changes a creature’s size, use Table: Changes to Statistics by Size to calculate changes to natural armor, Armor Class, attack rolls, and grapple bonus.
Hit Dice and Hit Points
Most templates do not change the number of Hit Dice a monster has, but some do. Some templates change the size of a creature’s Hit Dice (usually by changing the creature type). A few templates change previously acquired Hit Dice, and continue to change Hit Dice gained with class levels, but most templates that change Hit Dice change only the creature’s original HD and leave class Hit Dice unchanged.
If the Hit Dice entry in a template description is missing, Hit Dice and hit points do not change unless the creature’s Constitution modifier changes.
Initiative
If a template changes the monster’s Dexterity, or if it adds or removes the Improved Initiative feat, this entry changes.
Speed
If a template modifies a creature’s speed, the template states how that happens. More commonly, a template adds a new movement mode.
Armor Class
If a template changes the creature’s size, see Table: Changes to Statistics by Size to determine its new Armor Class and to see whether its natural armor changes. In some cases the method of determining Armor Class changes radically; the template description explains how to adjust the creature’s AC.
Base Attack/Grapple
Templates usually do not change a creature’s base attack bonus. If a template modifies a creature’s base attack bonus, the template description states how that happens. Changes to a creature’s Strength score can change a creature’s grapple bonus, as can changes to its size.
Attack and Full Attack
Most templates do not change a creature’s attack bonus or modes of attack, even when the creature’s type changes (the creature’s base attack bonus is the same as a creature of the original type). Of course, any change in ability scores may affect attack bonuses. If Strength or Dexterity changes, use the new modifier to determine attack bonuses. A change in a monster’s size also changes its attack bonus; see Table: Changes to Statistics by Size.
Damage
Damage changes with Strength. If the creature uses a two-handed weapon or has a single natural weapon, it adds 1½ times its Strength bonus to the damage. If it has more than a single attack then it adds its Strength bonus to damage rolls for the primary attack and ½ its Strength bonus to all secondary attacks.
Space/Reach
A template may change this entry if it changes the monster’s size. Note that this table does not take into account special situations such as exceptional reach.
5e Giving Monsters Class Levels Dmg 3
Special Attacks
A template may add or remove special attacks. The template description gives the details of any special attacks a template provides, including how to determine saving throw DCs, if applicable.
Special Qualities
A template may add or remove special qualities. The template description gives the details of any special qualities a template provides, including how to determine saving throw DCs, if applicable. Even if the special qualities entry is missing from a template description, the creature still gains any qualities associated with its new type.
Base Saves
As with attacks, changing a monster’s type does not always change its base saving throw bonuses. You only need to adjust them for new modifiers for Constitution, Dexterity, or Wisdom. A template may, however, state that a monster has a different 'good' saving throw.
Abilities
If a template changes one or more ability scores, these changes are noted here.
Skills
As with attacks, changing a monster’s type does not always change its skill points. Most templates don’t change the number of Hit Dice a creature has, so you don’t need to adjust skills in that case unless the key abilities for those skills have changed, or the template gives a bonus on one or more skills, or unless the template gives a feat that provides a bonus on a skill check.
Some templates change how skill points are determined, but this change usually only affects skill points gained after the template is applied. Treat skills listed in the base creature’s description as class skills, as well as any new skills provided by the template.
Feats
Since most templates do not change the number of Hit Dice a creature has, a template will not change the number of feats the creature has. Some templates grant one or more bonus feats.
Environment
Usually the same as the base creature.
Organization
Usually the same as the base creature.
Challenge Rating
Most templates increase the creature’s Challenge Rating. A template might provide a modifier to be added to the base creature’s CR, or it might specify a range of modifiers depending on the base creature’s original Hit Dice or CR.
5e Giving Monsters Class Levels Dmg 3
Treasure
Usually the same as the base creature.
Alignment
Usually the same as the base creature, unless the template is associated with a certain alignment.
Advancement
Usually the same as the base creature.
Level Adjustment
This entry is a modifier to the base creature’s level adjustment. Any level adjustment is meaningless unless the creature retains a high enough Intelligence (minimum 3) to gain class levels after applying the template.
Adding More Than One Template
In theory, there’s no limit to the number of templates you can add to a creature. To add more than one template, just apply each template one at a time. Always apply inherited templates before applying acquired templates. Whenever you add multiple templates, pay attention to the creature’s type—you may add a template that makes the creature ineligible for other templates you might want to add.
Advanced Monster Challenge Rating
When adding class levels to a creature with 1 or less HD, you advance the creature like a character. Otherwise, use the following guidelines.
Adding Class Levels
If you are advancing a monster by adding player character class levels, decide if the class levels directly improve the monster’s existing capabilities.
When adding class levels to a creature, you should give it typical ability scores appropriate for that class. Most creatures are built using the standard array of ability scores: 11, 11, 11, 10, 10, 10, adjusted by racial modifiers. If you give a creature a PC class use the elite array of ability scores before racial adjustments: 15, 14, 13, 12, 10, 8. Creatures with NPC classes use the nonelite array of: 13, 12, 11, 10, 9, 8.
Associated Class Levels
Class levels that increase a monster’s existing strengths are known as associated class levels. Each associated class level a monster has increases its CR by 1.
Barbarian, fighter, paladin, and ranger are associated classes for a creature that relies on its fighting ability.
Rogue and ranger are associated classes for a creature that relies on stealth to surprise its foes, or on skill use to give itself an advantage.
A spellcasting class is an associated class for a creature that already has the ability to cast spells as a character of the class in question, since the monster’s levels in the spellcasting class stack with its innate spellcasting ability.
Nonassociated Class Levels
If you add a class level that doesn’t directly play to a creature’s strength the class level is considered nonassociated, and things get a little more complicated. Adding a nonassociated class level to a monster increases its CR by ½ per level until one of its nonassociated class levels equals its original Hit Dice. At that point, each additional level of the same class or a similar one is considered associated and increases the monster’s CR by 1.
Levels in NPC classes are always treated as nonassociated.
Adding Hit Dice
When you improve a monster by adding Hit Dice, use Table: Improved Monster CR Increase to determine the effect on the creature’s CR. Keep in mind that many monsters that advance by adding Hit Dice also increase in size. Do not stack this CR increase with any increase from class levels. In general, once you’ve doubled a creature’s CR, you should closely watch any additional increases in its abilities. Adding Hit Dice to a creature improves several of its abilities, and radical increases might not follow this progression indefinitely. Compare the monster’s improved attack bonus, saving throw bonuses, and any DCs of its special abilities from the HD increase to typical characters of the appropriate level and adjust the CR accordingly.
| Creature’s Original Type | CR Increase |
|---|---|
|
|
| Aberration, construct, elemental, fey, giant, humanoid, ooze, plant, undead, vermin | +1 per 4 HD added |
| Animal, magical beast, monstrous humanoid | +1 per 3 HD added |
| Dragon, outsider, nonassociated class levels | +1 per 2 HD or 2 levels added |
| Directly associated class levels | +1 per level added |
| Other Modifiers | CR Increase |
| Size increased to Large or larger | +1 to CR |
| Monster’s ability scores based on elite array1 | +1 to CR |
| Monster possesses special attacks or qualities that significantly improve combat effectiveness | +2 to CR |
| Monster possesses special attacks or qualities that improve combat effectiveness in a minor way | +1 to CR |
| Template added | + template CR modifier |
Increasing Size
Generally, increasing a monster’s size increases its combat effectiveness. Large creatures gain increased Strength, reach, and other benefits. Apply this modifier if you increase a creature beyond Medium and in conjunction with any other increases.
Be careful, though. Monsters that benefit from a smaller size may actually lose effectiveness because of a size increase. Monsters that don’t benefit from size increases don’t advance in that manner for this reason.
Adding Special Abilities
You can add any sort of spell-like, supernatural, or extraordinary ability to a creature. As with a class level, you should determine how much, or how little, this ability adds to the creature’s existing repertoire. A suite of abilities that work together should be treated as a single modifier for this purpose. If the ability (or combination of abilities) significantly increases the monster’s combat effectiveness, increase its CR by 2. Minor abilities increase the creature’s CR by 1, and truly trivial abilities may not increase CR at all. If the special abilities a monster gains are not tied to a class or Hit Die increase, this CR increase stacks.
A significant special attack is one that stands a good chance of incapacitating or crippling a character in one round. A significant special quality is one that seriously diminishes the monster’s vulnerability to common attacks. Do not add this factor twice if a monster has both special attacks and special qualities.
Make sure to 'scale' your evaluation of these abilities by the monster’s current CR.
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Home >Bestiary >Rules for Monsters >
Contents
- Adding Racial Hit Dice
- Adding Class Levels
The following rules allow you to adjust monsters, increasing (or even decreasing) their statistics and abilities while still creating a balanced and fun encounter.
| Higher CR | Lower CR | Hit Point Change | AC Change | Attack Bonus Change | Damage Bonus Change |
|---|---|---|---|---|---|
| 1 | Less than 1 | 5 | 1 | 1 | 2–3 |
| 2 | 1 | 5 | 2 | 2 | 2–3 |
| 3 | 2 | 10 | 1 | 1–2 | 2–3 |
| 4 | 3 | 10 | 2 | 2 | 2–3 |
| 5 | 4 | 15 | 1 | 1–2 | 3–4 |
| 6 | 5 | 15 | 1 | 1–2 | 3–5 |
| 7 | 6 | 15 | 1 | 1–2 | 4–5 |
| 8 | 7 | 15 | 1 | 1–2 | 4–5 |
| 9 | 8 | 15 | 2 | 1–2 | 4–5 |
| 10 | 9 | 15 | 1 | 1 | 3–5 |
| 11 | 10 | 15 | 1 | 1 | 4–5 |
| 12 | 11 | 15 | 2 | 1–2 | 4–5 |
| 13 | 12 | 20 | 1 | 1 | 4–5 |
| 14 | 13 | 20 | 1 | 1 | 3–5 |
| 15 | 14 | 20 | 1 | 1 | 4–5 |
| 16 | 15 | 20 | 1 | 1–2 | 8–10 |
| 17 | 16 | 30 | 1 | 1 | 7–10 |
| 18 | 17 | 30 | 1 | 1 | 8–10 |
| 19 | 18 | 30 | 1 | 1 | 7–10 |
| 20 | 19 | 40 | 2 | 1 | 8–10 |
| 21+ | 20+ | 40 | 2 | 1 | 8–10 |
| Old Size* | New Size | Str | Dex | Con | Natural Armor |
|---|---|---|---|---|---|
| Fine | Diminutive | Same | –2 | Same | Same |
| Diminutive | Tiny | +2 | –2 | Same | Same |
| Tiny | Small | +4 | –2 | Same | Same |
| Small | Medium | +4 | –2 | +2 | Same |
| Medium | Large | +8 | –2 | +4 | +2 |
| Large | Huge | +8 | –2 | +4 | +3 |
| Huge | Gargantuan | +8 | Same | +4 | +4 |
| Gargantuan | Colossal | +8 | Same | +4 | +5 |
| * Repeat the adjustment if the creature moves up more than one size. | |||||
| Size | AC/Attack | CMB/CMD | Fly Skill | Stealth Skill |
|---|---|---|---|---|
| Fine | +8 | –8 | +8 | +16 |
| Diminutive | +4 | –4 | +6 | +12 |
| Tiny | +2 | –2 | +4 | +8 |
| Small | +1 | –1 | +2 | +4 |
| Medium | +0 | +0 | +0 | +0 |
| Large | –1 | +1 | –2 | –4 |
| Huge | –2 | +2 | –4 | –8 |
| Gargantuan | –4 | +4 | –6 | –12 |
| Colossal | –8 | +8 | –8 | –16 |
| Monster Role | Barbarian, Fighter, Ranger | Cleric, Druid, Sorcerer, Wizard | Bard, Rogue | Monk, Paladin |
|---|---|---|---|---|
| Combat | Key | — | — | — |
| Spell | — | Key* | — | — |
| Skill | Key | — | Key | — |
| Special | — | — | — | — |
| * This class is only key if its spellcasting levels stack with those possessed by the creature. | ||||
Adding racial Hit Dice to a monster is a similar process to building a monster from scratch. As additional Hit Dice are added, other abilities increase in power as well. Additional Hit Dice usually results in better attack bonuses, saves, hit points, and skills, as well as more feats. It can also include additional spellcasting capability and other powers.
Step 1: Plan the Monster
5e Giving Monsters Class Levels Dmg 2
When advancing a monster by adding racial HD, you should start by deciding what you want the monster to become. In most cases, this means merely a tougher, stronger version of an existing monster. Note the desired CR of the new monster. This is also the point at which you should decide whether the creature is going to increase in size. As a general rule, creatures whose Hit Dice increase by 50% or more should also increase in size, but GMs should feel free to ignore this rule if warranted by the individual creature or situation.
Step 2: Add Hit Dice
Next, determine how many Hit Points the base monster receives per Hit Die (see Table: Average Die Results for average results based on the die type). Using Table: Monster Advancement, add up all of the values in the Hit Point Change column for each increase using the Higher CR column. For example, if the base monster was CR 3 and the new monster is set to be CR 5, the total would be 25 hit points. Next, add additional Hit Dice to the monster to increase its hit points by the desired amount. Note that if the creature increases in size, its Constitution may also increase, as noted on Table: Size Changes, granting it additional hit points that might offset the need for additional Hit Dice (this also applies to any other Constitution increases).
These values are not absolute. Some monsters have fewer hit points than normal for a creature of their CR and rely on a higher AC or other defenses. Some creatures are primarily spellcasters and typically have fewer Hit Dice. When advancing your monster in this way, be sure to take these factors into account and adjust your monster accordingly.
Step 3: Modify Ability Scores
Once you have determined the number of additional Hit Dice possessed by the creature, use this number to modify its other statistics. Start with ability scores. For every 4 additional Hit Dice gained by the monster, add 1 to one of its ability scores. In addition, make any modifications to its ability scores based on an increase in size, as noted on Table: Size Changes.
Step 4: Choose Skills and Feats
When adding skills, check to see if the creature’s Int modifier changed. If it is unchanged, simply multiply the total number of ranks per Hit Dice gained by a monster of its type times the total number of added Hit Dice and add that number of ranks to its existing skills. If its Intelligence modifier has increased, perform the same calculation as if it had not increased and then multiply the change in its Intelligence modifier times its new total number of Hit Dice and add that number of additional ranks as well (adding new skills as needed to spend all of the ranks). If the creature changed size, make sure to adjust its Fly skill and Stealth skill bonuses (if any) as noted on Table: Size Bonuses and Penalties.
Next, give the creature additional feats. Creatures gain one feat at 1 Hit Die and one additional feat for every 2 Hit Dice above 1. Most additional feats should be focused on increasing the creature’s combat abilities, but metamagic feats and skill feats are also possible choices depending on the creature’s role.
Step 5: Adjust Statistics
Next, adjust the creature’s derived statistics, such as its initiative, AC, saving throws, melee and ranged attack bonuses, BAB, CMB, and CMD. Adjust any special attacks or qualities that are based on the creature’s size, Hit Dice, or ability scores. If the creature changed in size, be sure to adjust its AC, attack, CMB, and CMD accordingly (as noted on Table: Size Bonuses and Penalties). Table: Monster Advancement also tracks the average change to the creature’s AC, attack rolls, and damage rolls. Add up these values for each step of change between the creature’s original and new CR. If the creature changed size, make sure to make changes to its natural armor bonus, as noted on Table: Size Changes. If the creature does not meet these averages, you should consider adjusting its ability scores or Hit Dice to get it closer to the target.
Step 6: Compare to Existing Monsters
Finally, compare the new monster’s statistics to those presented on Table: Monster Statistics by CR for a creature of its adjusted CR. Note that if the original creature deviated from these values, the new one should do so in a similar fashion. For example, if the original creature had higher than normal hit points but a lower than normal AC, the creature should maintain that balance at a higher CR (even though its hit points and AC both increased).
Of all the methods of advancing a monster, adding class levels requires the most adjudication and careful comparison. Some classes truly add to the power and abilities of some monster types, while others do not. For example, adding levels of barbarian to a hill giant can be a great addition, whereas adding levels of sorcerer is less useful. When adding class levels to a creature, take the following three steps.
Step 1: Determine Creature’s Role
When adding class levels to a creature, the first step is to determine what role the base creature fulfills. There are three basic roles into which a creature might fall. A creature can fall into more than one role if its abilities are diverse.
Combat: This creature is designed to be good at melee or ranged combat with a weapon or its natural weapons. In either case, these monsters have a number of feats and abilities to enhance their combat prowess (or are good simply by nature of their Hit Dice and ability scores). If a creature does not possess many spells, special abilities, or skills, it is a combat monster.
Most animals, constructs, dragons, humanoids, magical beasts, monstrous humanoids, plants, and vermin fall into this role, as do some creatures of all the other types.
Spell: Spell creatures possess a large number of spells that allow them to attack or harass their enemies. These creatures usually have lower hit points and relatively weak attacks as compared to the averages for creatures of their CR. Note that creatures that only possess spell-like abilities do not fall into this role, and are usually considered combat or special.
Most dragons and outsiders fall into this role, but any creature that has a list of spells prepared or spells known likely falls under this heading as well.
Skill: Creatures of this type rely on skills (usually Stealth) to ambush or take down their prey. This also includes creatures who take advantage of the environment or spells, such as fog or invisibility.
Some aberrations, fey, magical beasts, monstrous humanoids, and outsiders fall into this role.
Special: Creatures that do not fall into any of the other categories usually rely on special abilities and powers to attack their foes. They might be tough or dangerous in physical combat, but the threat is greatly increased by their special abilities.
See monster roles for determining key classes.
Step 2: Add Class Levels
Once you have determined the creature’s role, it’s time to add class levels. The first step of this process is to modify the creature’s ability scores. Creatures with class levels receive +4, +4, +2, +2, +0, and –2 adjustments to their ability scores, assigned in a manner that enhances their class abilities. Creatures with NPC class levels do not receive adjustments to their ability scores.
Next, add the class levels to the monster, making all of the necessary additions to its HD, hit points, BAB, CMB, CMD, feats, skills, spells, and class features. If the creature possesses class features (such as spellcasting or sneak attack) for the class that is being added, these abilities stack. This functions just like adding class levels to a character without racial Hit Dice.
A monster with class levels always possesses treasure equal to an NPC of a level equal to the monster’s final CR (as calculated in Step 3, below). To determine the value of this gear, use the value listed for a heroic NPC of that level, as listed in Table NPC Gear. Once a total GP value is determined, follow the rules for outfitting an NPC as outlined in that section. Gear should help a monster with class levels remain challenging and retain statistics close to those presented on Table: Monster Statistics by CR.
What creatures get max hit points for their first level or first Hit Die? What creatures get favored class bonuses to hit points or skills?
Creatures whose first Hit Die is from a PC-appropriate character class gain max hit points for that Hit Die. The current list of PC-appropriate character classes is alchemist, barbarian, bard, cavalier, cleric, druid, fighter, inquisitor, monk, oracle, paladin, ranger, rogue, sorcerer, summoner, witch, and wizard (including archetypes, subclasses, and other variants of these classes).
Creatures whose first Hit Die is from an NPC class (adept, aristocrat, commoner, expert, warrior) or from a racial Hit Die (such as most monsters) do not get maximum hit points for that Hit Die.
All creatures with class levels (including those with levels in an NPC class or monsters with class levels) may select a favored class and gain the normal favored class benefits. Creatures never gain favored class benefits for racial Hit Dice.
For example, a humanwarrior 1 could select “warrior” as his favored class and take either the bonus hit point or skill rank for taking a level in that class. A normal bugbear with 3 racial Hit Dice and no class levels has no favored class and no favored class bonuses, but if that bugbear gained a level in rogue, he could choose “rogue” as his favored class and take either the bonus hit point or skill rank for taking a level in that class.
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Step 3: Determine Challenge Rating (CR)
Determining the final CR for a creature with class levels requires careful consideration. While adding a class level to a monster that stacks with its existing abilities and role generally adds 1 to its CR for each level taken, adding classes that do not stack is more complicated.
Table: Monsters with Class Levels gives general guidelines regarding which core classes add directly to a monster’s abilities based on its role (see Monsters by Role). Classes that are marked “key” generally add 1 to a creature’s CR for each level added. Classes marked with a “—” increase a creature’s CR by 1 for every 2 class levels added until the number of levels added are equal to (or exceed) the creature’s original CR, at which point they are treated as “key” levels (adding 1 to the creature’s CR for each level added). Creatures that fall into multiple roles treat a class as key if either of its roles treat the class as key. Note that levels in NPC classes are never considered key.