Project Nemesis is a fan driven website for games that use the One-Roll Engine (like Nemesis, Wild Talents, Reign and Monsters) or Chaosium's Basic Roleplay System (BRP) (like Call of Cthulhu) and the Delta Green setting.
Magic is by its nature transgressive: it breaks the laws of nature or
evokes power best left untouched. When a Sorcerer attempts magic beyond
their ability or purposely seeks out that knowledge, the magic they
wield corrupts their nature and attunes the Sorcerer more closely with
whatever dark nature magic has.
The source of this magic can be alien or otherworldly, demonic, a touch
of the fey or drake in one’s blood, the cold uncaring unknown, the
chilling wind of the undeath, or the pureness of chaos. Once the power
has been awakened within, once one has had a taste of power greater
than their own, once demons have whispered into their ears or the
limitless vistas of an ever-shifting reality of our own, one can tap
into that power to enhance their own magic.
The GM should determine where the magic comes from and how this power can be corrupting.
Acquiring Corruption
The first time a Sorcerer casts a spell where they fail to invoke the
spell but do gain a set beneath the Intensity of the spell, they have
glimpsed or summoned power beyond their own and their spell falters.
They gain their first Corruption Point. If they so choose, they can
then immediately use that die and roll it if they so desire to see if
they can make any sets.
Using Corruption
The Sorcerer now has avenue to a forbidden source of power which they
can use to power their invocations. Whenever a Sorcerer casts a spell,
they can choose to allocate any number of dice as a bonus to the roll
before the dice are rolled. These bonus dice should be in a different
color or rolled into a different pool. These dice can then be used to
create sets. If a Sorcerer has at least three Corruption, they can
replace three dice with an Expert die, although there are consequences
as noted below.
Based upon the exact nature of Corruption that the player has acquired,
Corruption might also be applicable as bonus dice to certain other
actions, as determined by the GM. These could be used as bonus die/dice
for certain skills. If the Corruption dice used for this fail to form a
set, they do not increase Corruption but create a complication to the
current scene or to a latter scene directly resulting from the
character’s misuse of their power.
Increasing Corruption
Whenever a Sorcerer commits Corruption dice to a roll and none of the
dice create a set that matches or exceeds the Intensity of that spell,
Corruption increases by one. Typically, Corruption dice must be
committed before the roll, but as soon as one’s corruption increases as
a result of gaining Initial Corruption or Increased Corruption from
Corruption dice failing to form any successful sets, the die resulting
from the increase can then be rolled and added to the set. If this new
additional die from the increase in Corruption does not form any sets,
it does not trigger an increase in Corruption. An Expert Die used in a
spell always triggers an increase in Corruption.
Alternative Means of Increasing Corruption
There may be other ways to increase Corruption besides failing at
spells while evoking corrupting power. What may increase Corruption
depends on what Corruption represents: a human sacrifice to demons may
increase Corruption for one Sorcerer, while turning one’s firstborn
over to the Fey may increase Corruption for another. How to increase
Corruption is something decided upon by the GM and the player. Making a
successful Forbidden Lore + Know test may give the PC insights into how
to do this.
Generally, an act increasing power must involve some sort of cost or
sacrifice, be it expressed mechanically through the game or socially
through the relationships with others in the game world. Any given act
should increase Corruption by +1. In nearly all cases, gaining
Corruption through this means should almost always be a consequence of
a player’s choices, not mandated by the GM as another form of “damage”
for something beyond the player’s choice. An exception, such as being
accidentally exposed to the insidious and uncontrollable influence of
chaos might be acceptable if both players and GM have agreed to this
beforehand. Even so, the gain of the last sixth point of Corruption
should always be a consequence of a decision made by the player.
Consequences of Corruption
The exact nature of the consequences is determined by the nature of
magic, but usually when Corruption reaches 6 the character is consumed
by their power in a dramatic manner and their fate is determined in the
current or next session as agreed upon by the player and the GM.
Individual increases in Corruption at the lower levels may also involve
some sort of consequence. The exact nature of these consequences is
contingent upon the nature of the forbidden power. Examples below.
Possible Consequences:
Each point of Corruption provides insight into the dark and terrible.
Each point of Corruption gives the PC the skill of Forbidden Lore and
every time Corruption increases, this skill increases. This may allow
access to new spells if suitable.
Alternately, rather than Corruption also creating a "Forbidden Lore"
skill, it could instead create a new "Sorcery" skill with access to a
new field of dark magic.
At each or every other stage, the PC may acquire an advantage or disadvantage.
The GM may tie the Corruption system to the Unnatural/Supernatural Madness Meter
A sample set of consequences tied to a particular magic is provided below:
Fey Blood:
The Nature of Fey’s Bood: There are some people whose blood conceals a
secret: they have the blood an ancient, older people long retired from
the world known as the Fey. It is this secret nature that has given
them the natural predilection towards Sorcery.
Corruption Idiom: The Fading or "Twilight"
Other Uses for Corruption/The Fading: The Fading may be used for any Charm or Command skill used to entertain or deceive as well as for Counterspell and Eerie.
01: Access to Forbidden Lore: The Fey
02: Gain advantage “Beauty 1”
03: Lose a Passion, -1 to any sincere interactions with humans
04: Lose a Passion, Gain Advantage: “Lucky”
05: Lose a Passion, Gain Problem “Unwholesome”
06: PC fades into the Fey World