FREQUENCY: Very rare ([Cold Wilderness Mountains])
FREQUENCY: Very rare ([Temperate Wilderness Mountains])
FREQUENCY: Very rare ([Dungeon Level VII])

NO. APPEARING: 1
ARMOR CLASS: 0 <sw, mw: 0>
MOVE: 36"
HIT DICE: 6+1
% IN LAIR: Nil
TREASURE TYPE: Nil
NO. OF ATTACKS: 1
DAMAGE/ATTACK: 3-12
SPECIAL ATTACKS: Energy and strength drain - see below
SPECIAL DEFENSES: Can only be hit by silver and magical weapons; and see below
MAGIC RESISTANCE: 50% and see below
INTELLIGENCE: Very
ALIGNMENT: Lawful evil
SIZE: M
LEVEL/X.P. VALUE: VII | 1,300 + 8

It is believed that only three or four of these creatures exist, having
been summoned originally to the PMP, and stranded
there, by an evil magic-user of high experience level who died as a
result of the strain of the summoning. Their actual plane of origin is a
matter of conjecture.  Their behaviour is completely dominated by
their need to inhabit the body of a character of 5th or higher level in
order to perform the complex spell-casting ritual which will return
them to their place of origin. Only a human body will give them the
necessary psychic frame of reference, so they attack only humans.

In appearance the magnesium spirit resembles a cylinder of white
flame, 5' tall and 3' diameter, with a wispy tail 5' long. However
they do not give off any discernable heat.

Moving at extraordinary SPEED, the spirit will approach a party containing
humans and quickly reach a position within 10' of its selected victim (chosen
at random from the humans present), in which position it will pause and flare up in a slit-second blinding
flash of white light. All who are within 20' and who are observng the spirit (including non-humans) must
make a saving throw versus petrification to escape blindness for 12 turns (two full hours). Treat the effects as
the [blindness] spell of the illusionist.

The spirit will then attack, automatically gaining initiative each round
even against hasted opponents.
If it scores a hit it drains one energy level (alt) and two points of strength from the victim (the latter recoverable
at the rate of 1 point per hour, the energy level drain being permanent); it also inflicts 3-12 hit points of damage.
Once it has hit
it is locked onto its victim's body and will merge gradually into that
body, draining energy and strength and causing 3-12 hit points of
damage per round as it does so. After two melee rounds of this merging
process, the only way to hit the spirit without harming its victim
is with holy water which will cause 2-7 hit points of damage to spirit
per vial full and also force it to abandon the merging process
(though it may attack the same victim or another human victim int he
next round). During the mergin process, the spirit causes damage
automatically, requiring no 'to hit' roll.

If the spirit has achieved three rounds of the merging process without
being forced to abandon its victim (i.e. two rounds during which it is
vulnerable to normal attack and one round during which it is vulnerable
only to holy water) it will have taken over its victim and the
human persona will have been negated. If the victim has five or more
energy levels (hit dice) at that time (since he will have lost four, one
from the initial attack and three from three rounds of the merging
process, he must have been at least 9th level before the attack) the
spirit will use the body to shriek out its spell, which takes 5 segments,
and then the body and spirit will vanish in a flash of light. The spirit
has gone back to its plane of origin, never to return.

If the victim has fewer than five energy levels remaining (i.e. was at
most 8th level before the spirit's first attack), the spirit will abandon
the body and seek another, turning to another nearby human (if one
is available) and commencing the attack process all over again on him.
The body of the first victim, now a mindless husk, will collapse and
will resist all ressurection attempts (though a powerful spell such as a [wish] will
bring back the victim if used properly).

The magnesium spirit can only be harmed by silver or magical weapons.
It has a 50% magic resistance as well as immunity to [sleep], charm, hold, paralysation, and [fear] spells.
It is vulnerable to holy water at all times, whether during the merging process or otherwise,
taking 2-7 hit points of damage per vial-full thrown onto it.
 

     by Nick Louth