Zombie
Spoiler Warning: This page contains spoilers which may affect your IVAN experience negatively
General
Zombies are lumbering, reanimated corpses. They are very prevalent throughout the world of IVAN and can be encountered as early as the first floor of the Underwater tunnel.
Zombies are very tenacious, they can continue to attack even when dismembered. A zombie will attach the lost limbs, including heads, of other humanoid creatures it encounters.
Zombies may also wield some weapons and other equipment, increasing their potency.
Zombie flesh is spoiled, you should not consume it or any of their severed limbs.
Necromancy
Zombies can be generated via necromancy. Necromancers can generate zombies, and if they are present you will often have to kill the necromancer to stop the flow of zombies.. These necromancers prove to be a problem in large areas where they may be difficult to find.
Level 6 of the Gloomy Cave focuses on undead, and there are a prodgious amount of them here. This is a large, one room floor where undead and necromancers will attack you from all sides. The necromancers will often create zombies, and it may do so from humanoid pets you carried into the floor with you.
You can create zombies individually with a wand of necromancy. Use the wand on a corpse of a fallen humanoid creature and it will raise as a zombie. This is a method of gaining zombies as pets. If you want to truly revive a fallen creature, however, you will need to use a wand of resurrection.
There is another roundabout way of necromancy - tame a proper necromancer. Zombies raised by friendly necromancers will automatically be friendly to you. But beware: while having a horde of undead warriors on your side can be useful in some circumstances, it can also be a royal pain. A newly-raised zombie does not 'know' most orders and cannot be given certain orders in the first place if it lacks a head. So unless you go around playing Drill Sergeant to every single friendly zombie, they'll wear and wield whatever they come across, follow you in crowds and generally make nuisances of themselves.
Disease
One of the biggest threats associated with zombies in IVAN is that of leprosy. If you are "feeling very ill" during or following a fight with a zombie, you've likely caught the disease.
A nasty way to cripple the defenses of Attnam is to lead a group of infected friendly zombies into town and set them loose; just be sure to heal yourself afterwords.