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.

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.

Type	Hit Die	Attack Bonus	Good Saving Throws	Skill Points1
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 HD2
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 HD2
Outsider	d8	HD (as fighter)	Fort, Ref, Will	8 + Int mod per HD
Plant	d8	HD ×¾ (as cleric)	Fort	2 + Int mod per HD2
Undead	d12	HD ×½ (as wizard)	Will	4 + Int mod per HD2
Vermin	d8	HD ×¾ (as cleric)	Fort	2 + Int mod per HD2
All types have a number of feats equal to 1 + 1 per 3 Hit Dice. 1 As long as a creature has an Intelligence of at least 1, it gains a minimum of 1 skill point per Hit Die. 2 Creatures with an Intelligence score of “–” gain no skill points or feats.

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
1 Repeat the adjustment if the creature moves up more than one size category.

Old Damage (Each)1	New Damage
1d2	1d3
1d3	1d4
1d4	1d6
1d6	1d8
1d8	2d6
1d10	2d8
2d6	3d6
2d8	3d8
1 Repeat the adjustment if the creature moves up more than one size category.

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. T

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

Changes from Base Creature	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
1 Do not apply this increase if you advance a monster by class levels. (Monsters advanced by class levels are assumed to use the elite array.)

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.