I missed my post yesterday so there are going to be two today.
whether human or elf, follow the track for learning spells as indicated
in the Swords and Wizardry (or Labyrinth Lord) manuals. Each spell they
have prepared they can perform once a day, and then they will need to
rest and prepare the spells again. This is the limit to what a
magic-user can perform safely. However, any magic-user can attempt to
cast any spell which they have already expended, successfully or not,
and risk corruption. Each time they attempt this, they must first roll
against an increasingly difficult threshold of success. The GM can set
the exact mechanic, but I think it would be reasonable to make the
caster roll under 50% on a percentile roll, and then each additional
time reduce the percentage by another 10%. In other words, if Elric the
Grey has already cast Magic Missile once, but is in a jam and it would
be very helpful to be able to cast it again, he may do so, only first
rolling under 50 on a d%. If Elric wants to cast Magic Missile again,
this time he must roll under 40, and so on.
On a failed roll for a second spell attempt, the magic-user
first takes the spell's level in HD damage. In other words, if a human
magic-user fails on a level 2 spell re-attempt, he immediately takes 2d4
damage; if he fails on a level 8 spell, he takes 8d4 damage, etc.
Depending on which version of the rules you are using, an elven
magic-user might take [x]d4 damage as well, or [x]d6 if the elf's HD is a
d6. This damage cannot be blocked or reduced in any way, and if this
reduces the character to zero or fewer hit points, they fall unconscious
immediately, but do not naturally deteriorate at -1 HP per round as
with bleeding out. However, if they are physically struck or hit by
another damaging attack and reduced to negative their level in hit
points, they will die as usual. If the damage they take from failing the
spell is enough to kill them, they will die.
In addition to this, they will take one permanent defect as a sign of
their corruption by magic. This should ultimately be determined by the
Game Master, but the extent of the disfigurement should reflect the
strength of the spell. A magic-user botching a Magic Missile, for
instance, might come out of the experience with permanently blackened
fingertips, or a slight lingering scent of tar or boiled cabbage. A
magic-user failing Confusion might suffer a permanent 2 or 3 point
reduction in Charisma, might randomly forget one of their prepared
spells for the day, or inadvertently attack an ally. A failure with Hold
Portal might cause doors to randomly lock or unlock, likely at
inopportune times. Regardless, the Game Master should keep note of these
and should not be afraid to use them when the players least expect it.
Certainly some spell failures will have more severe effects than others,
but that is all part of the gamble when re-rolling a spell.
Finally, if a spell is re-rolled after being expended and the result is a
failure, that spell may not be re-rolled again until it is prepared
again. In other words, a magic-user who continues succeeding against
cumulatively decreasing odds may continue using the spell, but a
magic-user who fails a re-roll loses the spell AND suffers a serious
deleterious effect. A failure after multiple successes might be more
"serious" in its sign of corruption to represent how hard the magic-user
had been pushing it, at the Game Master's discretion. It is also up to
the Game Master to determine whether a magic-user knocked unconscious by
their own spell backfire should be more difficult to rouse than a
character stunned by other damage.
The damage taken upon a failed re-attempt is representative of the
overexertion caused by the magic-user performing something "unnatural."
The spellbook is a profoundly magical and otherworldly sort of item, and
in preparing a spell, one provides an avenue for the "blowback" of the
spell to dissipate. Without the spell's place in the spellbook, the
recoil is more and more difficult to control. The corruption caused by a
failed spell attempt is representative of all of that potential,
formless magic energy being drawn out of the Aethers, but then the
magic-user losing control or focus after having become excessively
exhausted, and the energies misfiring backwards on the caster, with
strange and unpredictable effects.
However, "corruption" does not have to be negative. If one prefers, one
can make a percentile roll any time a spell re-roll is failed, with a 3%
or 5% (or something) chance that something beneficial happens instead.
Maybe a magic-user is attempting Magic Missile, only Fireball comes out
instead. Magic does not obey the same set of laws as everything else in
the world, so the Game Master is encouraged to allow unusual things to
This has not been at all play-tested, so I have no idea of the plausibility of these mechanics in a real game setting.
I'd hope that the danger of major corruption would be enough to offset a
magic-user from deviating too far from the ordinary 1-spell-a-day
mechanic, but it of course doesn't account for the player who is a
glutton for punishment and has no problem at all with putting all the
other players in a tight spot. This also assumes the "set and forget"
style of casting that does not first require a success or to-hit roll;
if using this style of mechanic, one can probably substitute a
cumulative -2 modifier on that to-hit roll each time the spell is