Modifiers

This modifier means that the creature is able to gain Class Levels. This means that the creature will also generally be intelligent, have goals in life, allies, treasures, and mundane and magical items appropriate to a creature of its power level. When giving Class Levels to a creature, many of their stats, such as BatCh, Saving Throws, Attacks, Parries, and so on may be modified based upon their attributes. Always take the most favorable result.
Note that giving creatures Class Levels significantly increases their power and their Encounter Rating. It also means that their primary attribute scores usually affect their abilities, but creatures that gain Class Levels do NOT gain additional hitpoints from those classes.
 
This modifier applies to normally Mindless creatures; Free-Willed creatures are capable of logical reasoning, developing plans and goals, and have a sense of self and often a personality. If a normally Mindless creature is Free-Willed, they are now somewhat vulnerable to Sleep/Charm effects and fail their Save vs. Sleep/Charm on a natural “1” - Vampires would be considered an example of a Free-Willed Undead.
 
Beings with multiple creature types take all traits common to both creature types. Generally, one will not find creatures of multiple types with directly conflicting abilities. So, an Undead Construct would not parry (assuming it is mindless), would be immune to radiation (as Undead are), and can be turned as an Undead. However, it generally best to make creatures only fall into one creature type: An Undead Construct that is almost entirely a robot should be treated as a Construct, while one that is little more than a skeleton with a weapon grafted onto an arm should be considered an Undead.