ABYSMAL REALMS HELP FILES

IMMUNITY

Immunities, resistances, and vulnerabilities have generated a lot of
questions.  This may help clear things up a bit.

The first concept is that there are different kinds of damage.  There is
piercing damage (e.g. daggers), slashing damage (e.g. swords), and bashing
damage (e.g. clubs).  Those are the three most common forms of damage.  Yet
more exotic types do exist, such as electricity, fire, cold, etc.

The second concept is that each of those damage types has three possible
flags that control the extent of damage taken:  immune, resistant, and
vulnerable.  Immune means no damage is taken.  Resistant means less damage
than normal is taken.  And vulnerable means more damage than normal is taken.

The third concept is that having multiple flags on the same damage type
results in an "averaging" of the damage that is done.  Thus if a character
has resistance to piercing and vulnerability to piercing, the result is
normal damage.  That is, they would be taking damage as if they had neither
resistance nor vulnerability to piercing.  The two cancel each other out.

The fourth concept is that multiple identical flags on the same damage type
do NOT add up.  Thus if a character has five items that all give resistance
to piercing and even one item that gives a vulnerability to it, then the end
result is normal damage.  The five items with resistance do NOT add up, they
count as a single flag giving resistance to piercing.  This works in reverse
also, so that if a person had five vulnerabilities to piercing and even one
resistance to it, then the result would be normal damage.

If a character has multiple flags on the same damage type, they combine as
follows:  IMM+RES+VULN=IMM, IMM+VULN=RES, RES+VULN=NORM

There are two special flags that need explaining.  The first is the "weapon"
flag.  This flag covers all wielded weapons.  The second is "magic" which
covers spells and spell-like effects.