The following lists categorize all of the monsters into their roles, as detailed in Monster Advancement. These roles indicate what types of character classes are treated as key classes for each monster.
Combat monsters are good at ranged and melee combat.
Spell monsters have an inherent ability to cast magic spells.
Skill monsters are particularly adept at ambushing prey, use sneak attacks, or have bard-like powers.
Special monsters have no key classes—their focus is on unique tactics and abilities.
Creatures listed as having “Any Role” do not use special rules when advancing via class level—they lack racial Hit Dice, and thus advance in level normally. All of the PC races fit into this category as well.
Creatures listed in the “No Role” category have no key classes—these are generally any creatures that are mindless or have an Intelligence score of 2 or lower. Unlike Special creatures (which also have no key classes), creatures in this category cannot gain class levels at all, and must advance using other methods. If a creature in this category gains an Intelligence of 3 or higher, the creature becomes a Combat Role monster.
Note that monster templates are not listed here—with the exception of skeletons and zombies (which lose their intelligence and thus have no key classes), a templated monster's key class is the same as the base creature's key classes.