Creating a monster is part science and part art. While most monsters follow a general pattern of their overall power and abilities as related to their Challenge Rating (CR), there are many exceptions. Some monsters, for example, have significantly more hit points or a higher AC than the average for their CR, but make up for this advantage by being weak in other areas. Other monsters have significantly higher average damage, but have a lower attack bonus.

The following guidelines are provided to assist in monster creation and to help balance a creation for its CR.

The first step in creating a new monster is to define its concept and role in the game. Generally, this involves picking the monster's CR, type, physical appearance, and manner of fighting. Once you have these basic pieces of information, you should find a number of similar monsters of the same type and roughly the same CR for comparison purposes.

Once you have a creature's type and CR determined, use Table: Monster Statistics by CR to determine its approximate statistics by CR. These values are a rough guideline only. You will notice that many of the existing monsters in this book do not follow these guidelines exactly. Most monsters excel in one of these areas, usually in the amount of damage dealt, but lag in one or two other areas to help balance them out. When referring to Table: Monster Statistics by CR, keep the following points in mind.

CR: This is the approximate CR of the monster. This number might change as design progresses.

Hit Points: This is the approximate hit point total for the monster. Note that creatures with particularly high Armor Classes or saving throws, or a number of resistances, might have a lower number. Outsiders and constructs typically have lower hit point totals.

Armor Class: This is the average Armor Class for a creature of this CR. When it comes time to design the creature's protections, keep this number in mind. Creatures with hit points above the average often have lower Armor Class values to compensate.

High Attack: This is the average total attack bonus for a creature of this CR. This value is for creatures that are primarily melee or ranged combatants. Creatures with a higher than normal average damage typically have a lower attack value to compensate.

Low Attack: This is the average total attack bonus for a creature of this CR that does not rely upon melee or ranged attacks to deal damage. This includes most creatures that rely on spells and spell-like abilities in combat.

Average Damage: This is the average amount of damage dealt by a creature of this CR if all of its attacks are successful. To determine a creature's average damage, add the average value for all of the damage dice rolled (as determined by Table: Average Die Results) to the damage modifier for each attack.

A creature that relies on melee or ranged weapons in combat should have average damage within the range of high and low damage.

A creature with higher than normal attack bonuses will often deal lower damage, while a creature with lower than normal attack bonuses will often deal higher damage.

Primary Ability DC: This is the average difficulty class (DC) for any spells, spell-like abilities, and special abilities (such as breath weapons) possessed by a creature of this CR that relies on such attacks in combat. If an ability is particularly powerful, it might have a lower DC to compensate.

Secondary Ability DC: This is the average DC for spells and special abilities for a creature that does not rely on such attacks in combat. Generally, a DC should not be lower than this number.

Good Save: This is the average saving throw bonus for a creature of this CR if the saving throw is one of the creature's good saving throws.

Poor Save: This is the average saving throw bonus for a creature of this CR if the saving throw is one of the creature's poor saving throws.

The next step in creating a monster is to determine the approximate number of Hit Dice it has. Hit Dice determine a wide variety of other statistics, including the creature's feats, skills, hit points, attack bonuses, and special ability DCs.

A creature's total number of Hit Dice depends on a number of factors, but the two most important are its CR and its type. Table: Creature Hit Dice lists the average number of Hit Dice for each creature type, depending on its CR. While many of the monsters in this book are close to these values, some are not. This is because they have higher or lower average hit points to balance out their Armor Class or resistances.

Now that you have the creature's average statistics, it's time to pick its size. Most creatures range in size from Small to Huge, but other sizes are not uncommon. A creature's size sets a baseline for its physical ability scores and its natural weapon damage (as noted in the Natural Attacks description in the Universal Monster Rules—see Appendix 3, pages 297–306). You should pick a size that fits well with the creature's intended role in the game and Challenge Rating. If you decide to give a creature an unusual size for its CR or HD, you should justify the unusual choice in the monster's description to account for the discrepancy—in most cases, such unusually sized monsters should be highly magical in nature. See Table: Size for more information on creature sizes and expected scores.

Minimum/Maximum CR: These values list the minimum and the maximum challenge ratings a creature of the indicated size should fall between.

Base Str, Base Dex, Base Con: These list the average scores for a creature of this size. Your specific monster's Strength, Dexterity, or Constitution might vary greatly from these numbers, but if they do, you should pay close attention to how these variances affect its other statistics.

Once you have determined a creature's size, type, and Hit Dice, it's time to move on to its ability scores. The bonuses granted from these ability scores should increase a creature's hit points, attack bonuses, and saving throws to the approximate values presented on Table: Monster Statistics by CR.

A creature's physical ability scores (Strength, Dexterity, and Constitution) should be relatively close to the base values presented on Table: Size, depending on its size. Creatures with a few Hit Dice but a high average hit point total should have a higher than normal Constitution.

A creature's mental ability scores (Intelligence, Wisdom, and Charisma) are largely defined by the creature's concept. The base for all of these abilities is 10. Creatures that rely on spells and spell-like abilities in combat should have one mental ability score that stands out (usually Charisma). Creatures incapable of speech have an Intelligence score of 2 or lower. Unintelligent undead, constructs, oozes, plants, and vermin rarely have an Intelligence score.

Using Table: Creature Statistics by Type, determine how many skill ranks your creature has based on its type and Hit Dice. Assign these ranks as determined by the creature's concept. A creature's class skills are determined by its type (see Creature Types). Creatures with a low Intelligence typically only have ranks in Dexterity- and Strength-based skills.

After you have assigned skills, it's time to assign the creature's feats. Each creature with an Intelligence score receives a number of feats equal to 1 + 1 per every 2 Hit Dice after the first (so, 1 at 1 HD, 2 at 3 HD, etc.). A creature must qualify to take a feat as normal. See Table 1–6 for a quick feat calculation chart.

Using Table: Monster Statitics by CR, Table: Creature Statistics by Type, and Table: Statistics Summary, you can now determine many of the creature's other statistics.

When building a creature's Armor Class, start by adding armor, shield, and natural armor bonuses to its Dexterity modifier. If a creature does not wear armor, give it a tougher hide to get it near its average AC. Remember that creatures with higher hit point totals might have a lower Armor Class, whereas creatures with fewer hit points might have a higher Armor Class. If a creature's Armor Class deviates from the average by more than 5 points, it might not be the right CR.

When determining a creature's attack bonuses, refer to the guidelines from Table: Monster Statistics by CR based on the creature's CR. If the bonus is too low, consider increasing the creature's Strength or Dexterity, or increasing the amount of damage it deals to above the average. If the bonus is too high, consider decreasing the creature's Strength or Dexterity, or decrease the amount of damage it deals. If this value is significantly different, and the creature is intended to rely on melee or ranged attacks, consider adjusting the creature's CR.

Use Table: Average Die Results to determine the number of damage dice, combined with damage bonuses, that the creature needs to reach the average damage for its CR. The creature might need additional or more damaging attacks to approach the average. Remember that creatures that primarily deal damage with other abilities, such as spells, do not need to meet the average damage for their attacks. You can also use Table: Average Die Results to determine a creature's average hit points. Remember that PC class levels provide the maximum number of hit points at 1st level.

Repeat this process for a creature's saving throws. If the saving throws are too high, consider altering the ability scores on which they are based.

When determining a creature's speed, first decide if it has any alternative modes of movement, such as burrow, climb, fly, or swim. Most Medium creatures have a base speed of 30 feet. Quadrupeds and Large creatures increase this by 10 feet each. Smaller creatures decrease this base speed by 10 feet. If a creature is particularly fast or slow, modify the base speed by 10 feet. Burrow and climb speeds are usually half a creature's base speed, while flying speeds are roughly double. Remember to give a creature the appropriate skills for any unusual movement methods.

Monsters are different from characters in that they can have all sorts of different special abilities and qualities. Each of these is tied closely to the creature's concept, allowing it to fill a specific role in the game. For examples, look at monsters in this book. Monsters should use abilities from the Universal Monster Rules whenever possible, instead of creating new yet similar abilities—when you do create new abilities, use the Universal Monster Rules as a template for how to present and create the new abilities.

Most special abilities that cause damage, such as breath weapons, give a save (Fortitude, Reflex, or Will depending on the ability). The DC for almost all special abilities is equal to 10 + ½ the creature's Hit Dice + a relevant ability modifier (usually Constitution or Charisma depending on the ability). Special abilities that add to melee and ranged attacks generally do not allow a save, as they rely on the attacks hitting to be useful.

Special senses and resistances to certain energy types are common in creatures of CR 5 and lower. Damage reduction, energy immunities, and regeneration are more common in creatures above CR 5. Spell resistance and immunities become more common above CR 10. As a general rule a creature's spell resitance should equal its CR + 11.

A creature should have an amount of treasure appropriate to its CR. See Table: XP and GP Values by CR for a list of treasure totals based on CR. For some creatures, their treasure consists of the loot from their recent meals strewn across their lairs, while for others it consists of a greed-fueled hoard or even gear it uses in combat. Make sure to account for any weapons or armor that the creature is using, as determined by step 7.

Now that you have all of the creature's statistics sorted out, it's time to fill in all the details—such as name, alignment, space, reach, environment, and ecology—as you see fit.

The following rules allow you to adjust monsters, increasing (or even decreasing) their statistics and abilities while still creating a balanced and fun encounter.

A template is a set of rules that you apply to a monster to transform it into a different monster. All templates give precise directions on how to change a monster's statistics to transform it into the new monster.

Acquired Templates: Some templates, like the lich, are the results of a creature's choice and desire to transform. Others, like the ghost template, are the result of an external force acting upon a creature (for example, when a tormented person dies and becomes a ghost). Yet in both cases, the template changed a creature well after its birth or creation—these types are called "acquired templates," and can be added to a creature at any time during its existance.

Inherited Templates: Some templates, such as the half-dragon and half-fiend templates, are part of a creature from the beginning of its existence. Creatures are born or created with these templates already in place, and have never known life without them. These types of templates are called "inherited templates."

Simple templates can be applied during the game with minimal effort. This makes it easy, for example, to deal with celestial and fiendish creatures conjured in the heat of battle by summon monster spells.

All simple templates have two categories of changes. The "quick rules" present a fast way to modify die rolls made in play to simulate the template's effects without actually rebuilding the stat block—this method works great for summoned creatures. The "rebuild rules" list the exact changes you make to the base stat block if you have the time to completely rebuild it—this method works best when you have time during game preparation to build full stat blocks. The two methods result in creatures of similar, if not identical, abilities.

Creatures with the advanced template are fiercer and more powerful than their ordinary cousins.

Quick Rules: +2 on all rolls (including damage rolls) and special ability DCs; +4 to AC and CMD; +2 hp/HD.

Rebuild Rules: AC increase natural armor by +2; Ability Scores +4 to all ability scores.

Celestial creatures dwell in the higher planes, but can be summoned using spells such as summon monster and planar ally. A celestial creature's CR increases by +1 only if the base creature has 5 or more HD. A celestial creature's quick and rebuild rules are the same.

Rebuild Rules: Senses gains darkvision 60 ft.; Defensive Abilities gains DR and energy resistance as noted on the table; SR gains SR equal to new CR +5; Special Attacks smite evil 1/day as a swift action (adds Cha bonus to attack rolls and damage bonus equal to HD against evil foes; smite persists until target is dead or the celestial creature rests).

Creatures with the fiendish template live in the Lower Planes, such as the Abyss and Hell, but can be summoned using spells such as summon monster and planar ally. A fiendish creature's CR increases by +1 only if the base creature has 5 or more HD. A fiendish creature's quick and rebuild rules are the same.

Rebuild Rules: Senses gains darkvision 60 ft.; Defensive Abilities gains DR and energy resistance as noted on the table; SR gains SR equal to new CR +5; Special Attacks smite good 1/day as a swift action (adds Cha bonus to attack rolls and damage bonus equal to HD against good foes; smite persists until target is dead or the fiendish creature rests).

Creatures with the giant template are larger and stronger than their normal-sized kin. This template cannot be applied to creatures that are Colossal.

Quick Rules: +2 to all rolls based on Str or Con, +2 hp/HD, –1 penalty on all rolls based on Dex.

Rebuild Rules: Size increase by one category; AC increase natural armor by +3; Attacks increase dice rolled by 1 step; Ability Scores +4 size bonus to Str and Con, –2 Dex.

Creatures with the young template are immature specimens of the base creature. You can also use this simple template to easily create a smaller variant of a monster. This template cannot be applied to creatures that increase in power through aging or feeding (such as dragons or barghests) or creatures that are Fine-sized.

Quick Rules: +2 to all Dex-based rolls, –2 to all other rolls, –2 hp/HD.

Rebuild Rules: Size decrease by one category; AC reduce natural armor by –2 (minimum +0); Attacks decrease damage dice by 1 step; Ability Scores –4 Strength, –4 Con, +4 size bonus to Dex.

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.

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.

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.

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.

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.

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.

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 CR, 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.

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.

A list of monster roles for determining key classes appears in Appendix 13.

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 CR, 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 1-1: Monster Statistics by 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. 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.