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Adding Class Levels

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Adding Racial Hit Dice

Source Pathfinder RPG Bestiary pg. 295
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

Source Pathfinder RPG Bestiary pg. 295
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

Source Pathfinder RPG Bestiary pg. 295
Next, determine how many Hit Points the base monster receives per Hit Die (see Table 1–5 for average results based on the die type). Using Table 2–1, 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 2–2, 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.

Table 2-1: Monster Advancement

Higher CR	Lower CR	Hit Point Change	AC Change	Attack Bonus Change	Damage Change
1	Less than 1	5	1	1	2-3
2	1	5	2	1	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

Table 2-2: Size Changes

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.

Step 3: Ability Scores

Source Pathfinder RPG Bestiary pg. 296
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 2–2.

Step 4: Skills and Feats

Source Pathfinder RPG Bestiary pg. 296
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 2–3.

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.

Table 2-3: Size Bonuses and Penalties

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	+6	-8	-16

Step 5: Statistics

Source Pathfinder RPG Bestiary pg. 296
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 2–3). Table 2–1 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 2–2. 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: Comparison

Source Pathfinder RPG Bestiary pg. 296
Finally, compare the new monster’s statistics to those presented on Table 1–1 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).

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