Zombies are not enemies in the game, but rather a special type of player status that can only be attained at the beginning of the game. When your player dwarf is created as a result of the character creation process, the game assigns a hit point value of -1, 0, 1, 2, or 3. The player has a 4 in 5 chance of getting 3 hit points; if they do not, they then have a 3 in 4 chance of getting 2, then a 2 in 3 chance of getting 1. If all of these come up negative, the player has an equal chance of receiving either 0 hit points (resulting in a Zero-Move Death) or -1, resulting in what is informally called Zombie Status.
Pros and Cons of Zombie StatusEdit
When the zombie player takes damage from an enemy, it continues to drive his hit points "down": -2, -3, and so on, depending on the damage dealt. This makes the player functionally invulnerable to physical damage. The player is also invulnerable to God's dreaded smite attack, which functions by dealing physical damage equal to the player's max hit points (for example, subtracting -1 from -1 results in -2, a stronger, healthier, happier zombie). This makes a zombie especially desirable in the game's final level.
Zombies are, however, "vulnerable" to healing spells, which will add positive integers to their hit points value, and must account for the game's auto-recover mechanic; once they hit zero, the player will die. This makes the "mating levels" (20 through 23) especially dangerous for zombies. Danger also comes from stupid monsters. Also if a creature has a heal beam and is attempting to heal a creature which you are standing in front of.
As of the December 2010 release, zombies also have to contend with clerics.
How it WorksEdit
It is impossible to get Zombie Status after beginning the game; damage will never reduce a positive HP below 0, because damage can never exceed one's current hit points.
It should be noted that the game never refers to the player as a zombie or uses the term "Zombie Status"; the negative hit points trick is actually a bug that was embraced by the community and never removed.
Because the odds are stacked in favour of 3, 2, or 1 hit points, some players try to produce deliberately star-crossed or unlucky dwarfs in the character creation stage. Because this has just as much chance as ending up with 0 hit points, and that star-crossed characters with positive hit points are highly susceptible to God's smite attack, deliberately trying to create a zombie is tricky and frustrating business indeed.
Theoretically, it's possible to produce a zombie through several generations of mating, but since the She-Dwarfs of the mating levels are extremely sturdy (upping the odds that you'll get 3 hit points to start), the odds are stacked against it.