Undead, as defined in this guide, are people or creatures who were once living but were ressurected after their death and possess a physical form. They are kept "alive" by dark magic and their behavior greatly varies depending on what kind of undead they are.

Zombies are humans who have been ressurected after being mostly decayed. Their brains are non-functional and have no consciousness whatsoever. They are normally utilized for petty work like meat shields or servants.

Zombies, essentially, are brain-dead. They rely solely on animalistiic instincts and whatever muscle functionality they have left to get around. They are vile and savage, to say the least. Plus, they smell awful and can actually be identified from an impressive distance because of it.

Due to their stupidity and their inability to hide, they can be found anywhere.

Zombies are actually somewhat easier to deal with than a living human being. Their accuracy and coordination is off and they move at about half the speed of your average human. However, they have no restraint. Therefore, nothing is stopping them from throwing themselves at you— or, at least, trying to. Another problem is that they don't feel pain and, ergo, cannot be physically discouraged to stop fighting. Best strategy is to completely destroy the body, otherwise it'll keep getting back up. It isn't that hard to do due to their flesh and muscles being softened by decay.

Ghouls, while often confused with such, are not zombies. They are dead humans who have been ressurected by a curse (which is, admittedly, derived from necromancy.) Ghouls, unlike zombies, are living souls inside dead bodies. They don't decay over time and are actually stuck in the stage of decomposition they were in when they died.

Ghouls act similarly to humans but tend to have more violent tendencies. They are not brain-dead like zombies. They can restrain their ferality to an extent so don't piss them off. When provoked, they can devolve into an animalistic rage and still maintain consciousness, making them extremely dangerous.

Ghouls can be found anywhere. Where they live depends more on their personality than any other factor.

Ghouls are usually pretty civil but there are chances one could attack you. If you are attacked by one, it's more than likely that they are hungry and unable to restrain their thirst for blood. Ghouls usually act on emotion and impulse so you can easily negotiate with one. Hell, give them food, even. If it's good enough they might even call you a friend. However, if you must kill one, take the same route of action as you would with a zombie. Simple dismemberment wouldn't work so you have to mutilate the body as much as you possibly can. They are also weak to fire and ice.

Liches are a powerful, formidable, form of undead that possess many different forms of magic depending on how they died. They have full control over their minds and have retained all of their memories from before their death. More often than not, they are cultists who infused themselves with necromancy to ensure immortality.

Liches are often times level-headed and wise but don't let this fool you; their strength knows no bounds.

Liches usually are found in dark, isolated, places like caves or bunkers. Wherever they are, though, is made frigid due to their natural demonic aura.

Liches are immune to almost every type of conventional offense. Your best bet for killing one is utilizing any kind of holy imagery or fire.