Some common Information about various common monsters and enemies that people of The Maw know:
Most undead were once living. Knowing details about the phase of existence that preceded a creature’s undeath is often invaluable in determining its motives.
Holy water damages undead as though it were acid. Distributed by goodly religious orders the world over, holy water is the only line of defense against undead for many commoners.
Undead are invariably evil, as are the means to create such beings.
Undead are healed by negative energy and harmed by positive energy.
Undead are immune to numerous magical effects, including mind-affecting effects and abilities that affect a creature’s physical constitution.