General Guidelines
1. Each individual monster class should be presented as a basic race (Warforged Equivilent) followed by a class.
2. A good target for the number of levels a class should have is the monsters CR. However, if the class seems too weak you should compress the levels.
3. Each type of monster race may have several classes, to represent divergent abilities.
4. Monster Classes are treated as PRCs but with only a racial requirement, this means if you reincarnate or something you will lose class features. This is to prevent multiclassing between races. There are however other ways of doing this.
5. Racial immunities (construct, undead etc) should be granted in the base race. However, strong racial traits may mean that the base race will have few abilities.
6. The Base race should be no larger than medium and no smaller than Small.
7. The first size change in a class should be no earlier than level 4 and the second shouldn't be before level 8.
8. The racial mods of your class should be equal to the base monsters ability scores -10 or -11 to get even modifiers. Alternate classes for the same race use the same total but may alter the distribution
9. Only ever give out racial modifiers in even numbers.
10. Certain abilities don't really work for player characters until extremely high levels. You can delay an ability (or uses of an ability) until higher levels. For example the Succubus Seductor gets Greater Teleport at level 7 but does not get it at will until they have 17 HD.
11. To make the base race balanced you may need to give it negative ability mods even if the actual monster has none. Just make up the difference in the class.
12. Monsters generally shouldn't get a spell like ability at will before a wizard could cast the same spell.
13. Each monster has an attribute focus, This should be stated in the class, after weapon and armor proficiencies but before class abilities using this text: "Attribute" Based: All of the abilities gained in this class that require a save have a DC of 10 + 1/2 HD + "Attribute" mod. Caster Level is always equal to HD unless otherwise noted. This saves a lot of repetition.
14. BAB and Saves should be based off the monsters role. Spellcasters get 1/2 BAB and 1 good save, Melee get full BAB and three good saves. Everyone else gets mid BAB and 2 good saves. Melee classes have a max of 5th level spells, Spellcasters can have any and everyone else is capped at 7th level.
15. Skill points are also based off role. Spellcasters are capped at 2/level, melee at 4/level and everyone else is uncapped.
16. Every monster should speak Common provided it is capable of speaking at all.
17. Every monster (provided it has ability bonuses higher than +6 total) needs to include this below its weapon and armor proficiencies:
Ability Bonuses: A CLASS is REASON, their physical and mental abilities greatly surpass those of most humans. To represent this they have enhanced stats given in the table above. These bonuses are Enhancement bonuses and thus do not stack with most items that increase your ability scores. All bonuses on the table are cumulative.
