"Call of Cyberthulhu"
an unofficial CoC modification for cyberpunk genre gaming
by Sandy Antunes (email@example.com)
Chaosium's Call of Cthulhu has solid mechanics for interacting with both the
mundane and the bizarre. Extrapolating this to the Cyberpunk genre is very
straightforward. The main alterations are: addition of new skills and gear
(including cybernetics), slight modification of the combat system to intensify
the experience, and provision of a "future history" to provide a preliminary
The cyberpunk setting assumes a near-future setting, most appropriate
with the Cthulhu Now rules. It is entirely optional whether this setting
includes the Cthulhu Mythos at all, as the system is strong enough to work
without it. Without Cthulhu, Sanity is still a relevant statistic, as
Augmentation to the human form is available in two formats-- standard
Cybernetics, which are machine parts designed to be grafted onto the human
body, and Biotech, which are organic devices created to be incorporated into
the human body.
The standard CoC statistics all apply. "Education" can be relabeled
"Training", to indicate both college learning and learning on the streets.
"Sanity", especially for a non-Cthulhu game, may be renamed "Humanity", as
it will serve as a measure of how much cybernetics a person may incorporate
Adding cybernetic and biotech brings benefits, but also costs in
Sanity(/Humanity), indicating that the person has lost a little of their
touch with human reality by assimilating technology so much. In a non-Cthulhu
setting, this merely indicates one's empathy with human concerns. In a
Cthulhu setting, a lowered sanity can be quite significant-- people loaded up
with tech tend to fall to pieces quicker when faced with non-technological
menaces which defy reason. Sanity(/Humanity) also defines how much hardware
a person can add on and still remain "human".
The following skills are useful for a cyberpunk setting:
Computer Use (from 'Cthulhu Now') (25%): required for using any
computer, as computers are an integral part of society.
Computer Tech (0%): This includes both software and hardware creation
and modification, for computers and cyberwear.
Cooking/Bartending (10%): Bartending is added to the idea of a Cooking
skill to reflect the general lifestyle in cyberpunk-- a lot
hanging out at bars.
Interrogation (0%): Always a useful skill, includes detecting lies.
Mechanical/Robotics (20%): This combined skill reflects both general
mechanical aptitude and ability to repair or work with
the mechanical parts of cybernetics (but not the human part).
Pharmacology (0%): Important subdivision of Medical, for the cyberpunk
world. Default is 0%.
Battlesuit (0%): The ability to use powered armor, exoskeletons, etc.
Netrunning (0%): Required for people who will directly link into the
information Net (i.e. "Netrunners"). More on this later.
BioEngineering (0%): The equivalent of mechanical aptitude for the
field of biotech, bioengineering, or genetics.
Cybernetics (0%): A mix of mechanical skill and medicine, is required
for doctors who actually install or repair cybernetics.
Drive CyberRig (10%): A Drive skill, for 'riggers' who cybernetically
link to the equipment they operate (often trucks, gun turrets).
Heavy Machine Ops (10%): A catch-all for operating non-cybernetic
Tracking (10%): The ability to find or follow someone.
Brief Technology Skills example
Jerry the Rigger had his truck lit on fire, his cybernetic arm crushed
and torn off, and his biotech eye burned out. Someone with Mech/Robotics
could easily fix his truck, and could fix the damage to the arm, but couldn't
really reattach it. Someone with Cybernetics could both fix the arm and
reattach it, but would have a hard time fixing the truck. Someone with Medical
would be able to reattach the arm, but not fix the arm or the truck. None of
them could fix the eye, but Medical or Cybernetics could try to reattach it.
Biotech could fix the eye and reattach it, but not really do anything for the
arm or truck. Simple, yes?
New Weapons Skills
Not much is needed in the way of new weapons. "Staff/Stick" (10%)
includes most ideas like stunning billy clubs and such. "Blackjack" (25%)
refers to use of a blackjack or cosh (for rending people unconscious). "Bite"
(20%) becomes useful for people who augment themselves, as does "Claw" (25%).
Long range weapons may be added as desired, three to add are: "Tasp" (20%), a
weapon which gives a jolt to the pleasure (or, if designed, pain) center of
the brain from a distance, "Laser", for any beam weapons, and "Launchers",
a catch-all for the rocket/grenade-launcher class of weapons.
Implanted Options and Cybernetics
Abilities and gear can be added directly to the character's body by
spending skill points, just as with buying skills. More things can be added
than I can list, here is a start. Two types are available-- Cybernetics (your
standard technology, metal and plastic), and Biotech (more advanced and user-
friendly). Biotech costs 50% more than Cybernetics, but is less prone to
disruption and outside disturbances. For example, a really big magnet can
play havok with a metal/plastic arm, but a biotech arm is safe. Biotech is
also more subtle, and less likely to be noticed or detected by equipment.
Adding tech reduces one's Sanity(/Humanity), to calculate just divide the
number of skill points spend on gear (base cost, not including the 50% addition
for Biotech) by 5, then subtract (Biotech costs more to "buy", but doesn't
cost more for sanity.) Thus Jerry the Rigger can buy a cyber arm for 20 skill
points (costs 4 sanity), or a biotech arm for 30 skills points (still only
costs 4 sanity).
Options below give the cost (for standard Cybernetics) and advantages.
Items that give 'special stuff' give obvious benefits which are impossible
without them, for example, telescopic eyes would allow one to see very far.
Bonuses to "notice" are to the "Spot Hidden" skill.
Cybernetic Eyes: cost = 25 pts, adds no bonuses but you can add options
Options once you have cybernetic eyes (bonuses are cumulative):
Hearing enhancement: cost = 25 pts, +15% to Listen skill,
each additional +10pts = +15% to Listen skill.
Smell enhancement: cost = 20 pts, +10% to Notice, +10% to Tracking,
some poison detection.
Enhanced reflexes: cost = 20 pts for each +1 added to Dexterity.
Netrunning rig: cost = 30 pts for the basic rig (required to netrun)
or 70 pts for the enhanced rig (see Netrunning rules)
Socket jack: cost = 10 pts, allows use of 'skill chips' as well as the
ability to be linked into machinery.
Embedded weapon: cost = 20 pts if you have a cybernetic/biotech limb,
or 40 pts otherwise.
Cybernetic limbs: arms and hands add to Str or Dex, legs to Con or Dex
- IR (Infrared) option, 20 pts: adds +15% to notice
- Telescopic option, 14 points: adds +5% to notice plus 'special stuff'
- UV (Ultraviolet) option, 15 pts: adds +10% to notice
- X-ray option, 20 pts: adds +10% to notice plus 'special stuff'
- Microscopic option, 15 pts: adds +5% to notice plus 'special stuff'
- Night Vision option, 20 pts: allows full night vision
Netrunning: Only people with "Netrunning" skill and a Netrunning rig can
Netrun. To make a Run, they must first connect with the Net. This requires
two things-- a place to connect to, and a successful netrunning roll. If
they have the basic netrunning rig (above), they must remain at the location
where they connected for the Run. The enhanced rig allows encoded remote
connecting so they can be mobile (and remain with the party) while doing a
run, and it is HIGHLY recommend because 1) it is easier for the player,
2) it is easier for the gamemaster, 3) other NPC netrunners will laugh at
anyone too amateur not to have the enhanced rig, hurting your reputation.
Netrunning is a whole story in and of itself. To prevent a
simplified version of the system I used, there were two types of runs.
- cost = 20 pts/limb (includes hand or foot), with no bonuses,
10 pts/hand (or foot), with no bonuses.
- Each +1 of Str or Con or Dex the limb provides costs 10 pts.
- Limits: one hand = max +3 in bonuses, both hands = max +6 in bonuses
one arm/leg = max +4 bonus, + one hand = max +7 bonus
one pair = max +10 bonus, + one hand = max +13 bonus
one arm + one leg = max +8 + one hand = max +11
one pair + one arm/leg = max +14 + one hand = max + 17
2 pair = no limits
The rest, like all good cyberpunk games, is Atmosphere and Attitude. One of
the best advantages of using the CoC system for CP is that you always have
the option of expanding the game into the Mythos, anytime the players start
to get too set in their ways... Any questions, feel free to email me
- Information. Player rolls under their netrunning skill to make the
connection. This gives them a certain number of queries, or 'cycles',
before their connection is traced by security-- they could ask that many
'basic information' questions (ex, "I look up the name 'Jerry'".) They are
then given a basic line of information (ex, "Jerry "Bob" Hills, licensed
rigger, available for Hire") and a password to crack (a bit like hangman).
Each cracking attempt costs 1 'cycle' (remember, when they run out of
cycles they may be detected), and success yields more information-- at
the very least, an address, arrest record, and credit account. Depending
on their other skills, they can attempt a Task against that person...
- Tasks. Player wants to do an action-- penetrate security, destroy an
account that they have the credit number for, etc. (TBD)
Combat is essentially "hit them better than they defend".
your "to hit" roll by more than they make their "dodge" roll (if they are
able to dodge). For Cyberpunk, this gives a big edge to the faster player,
as is appropriate. Also, for combative netrunning, this "do it by more"
system applies for the PC netrunner going up against the NPC netrunner.
Each player is allowed two "actions" per combat round. This is generally
assumed to be one attack and one defense (typically "Dodge"). You are
allowed to Dodge as many attacks as come at you. Dodging while occupied
with another task (driving, wiring up a robot, etc) is at 1/2 your normal
Dodge skill. If you wish, you can do a double attack (but not be able to
defend), or do a double defense (not attacking, but able to use another
weapon to parry or to seek cover-- note that you can't "double Dodge", the
extra defense must be something other than Dodge). You can also choose to
aim and fire, giving up any defense. Aimed shots, if they hit, hit where
You must make your attack roll by better than they make their defense roll
for the attack to hit. If it hits, there is a chance it will miss due to
cover (see below) or reduced by armor (see section in CoC manual on armor).
Cover is often a factor in combat. The Keeper will decide the relative value
of cover and adjust "hits" accordingly. For non-aimed shots, cover is just
a percentage chance of hitting the person (instead of the cover) if the shot
hits. Aimed shots never hit cover.
People using cover are allowed their normal Dodge (which represents them
ducking out of the line of sight), even for aimed shots.
Typical values of cover are:
Inside a normal apartment, shooter outside across street = 50%
Standing behind a corner shooting at someone down an alley = 20%
Standing on a roof, shooting down = 40%
Standing behind a car = 50%
Hiding = generally reduces the chance of being hit by 1/2, for example,
40% cover implies 60% chance of being hit, so hiding increases the cover
to 70% (40 + 60/2). This assume you are not fighting but still trying to
keep track of the situation. If you want to totally Cower behind cover,
you a 1/3 reduced chance of being hit, but will be totally clueless as
to the situation (who is there, where they are, what is happening)
Most vehicles provide at least some cover in combat. The following are
guidelines for dealing with this, when someone is trying to shoot the
person (it is easy to hit the vehicles!):
Car: 50% chance a non-aimed shot will hit the car, not the person targeted
Motorcycle: 15% chance a non-aimed shot will hit the bike, not the person
Truck: 60% chance a non-aimed shot will hit the truck, not the person
A Rigger is a person who hooks themselves directly into a machine to use it.
Through a standard Rigger's interface, the person becomes almost one with the
machine, increasing their ability and speeding their response time. This
mix of person and technology gives the Rigger an edge over the manual operator.
The most common use of rigging is Driving-- truck, motorcycle, or pursuit
cars in particular benefit from the options and speed of rigging.
The basic rules of rigging are thus:
Rigger items confer extra abilities, for example, radar or early warning,
Quality rigger items add to the Rigging skill (typically +5 to +25%),
Rigging allows you two attempts to succeed at any task-- first, you roll
against natural skill; if this fails, you roll against Rigging to see
if the machine/person interlink is able to force a success. For example,
a driver with a 75% Drive and 50% Rigging in a rigged vehicle trying to
jump Snake River Canyon has to fail a roll of 75% AND a roll of 50% before
there are any problems-- so the odds are 80% in her favor. If her bike
is quality and adds 25% to her Rigging skill, this means the odds are 85%
in her favor,
In addition, riggers may use another (single) skill of theirs, while
at No Penalty (as long as the skill is physically possible.) This is
because the item handles most of the minor details, leaving the rigger
free to spend their attention elsewhere. So shooting, first aid, computer
library use, photography, and many other skills are possible while rigging.
The only universal exception is Netrunning-- due to the brain's bandwidth
limitations, you cannot effectively use a Netrunning rig and a Rigger's rig
simultaneously without penalty.
Jason the Rigger has a Drive skill of 55%, a Rigging skill of 55%, and a
dodge skill of 105%. Jason is driving his Rigged motorcycle, a
Harley-Davidson 1200 with direct-input controls, CoolLock autosteer, ProxyRite
proximity alarms, passive AI control support, submillimeter wave detectors for
guidance, UnSeen stealth design, heat signature minimization, AI-controlled
weapons support, an autoturret, and armor. The Keeper has rated the bike as
On this bike, Jason's effective Driving skill is 65%, his Rigging skill is
80%, and his Dodge skill is (105/2)+20, or 72%, not to mention he has a
30% chance that the bike armor absorbs any hits to him. In general, his
chance of succeeding in driving/rigging is better than 85%. He has a 70%
chance of hitting and gets 3 shots per round using the autoturret. While
driving, dodging, and firing the autoturret, he is still allowed one more
reasonable action (such as Navigate or Photography or using his shotgun)
at normal skill.
- adds 10% to Driving (CoolLock autosteer, very well designed bike)
- adds 25% to Rigging (excellent interface and AI driving control support)
- no visibility penalty for Driving or using the autoturret at night or in rain
(due to Submm)
- Stealth mode: Has an intrinsic 70% chance of not being heard (Sneak) by
anyone further than short range away when in Stealth mode, however, in
Stealth mode top speed is 50KPH.
- Submm detectors: automatic detection/location (Spot Hidden) for any living
being or moving object, dog-sized or larger,within medium range. 80%
chance of detecting any road obstructions before they present a hazard.
- Proximity alarms: Adds 20% to "Dodge" if attacked (note that "Dodge" while
on a vehical is normally halved).
- Autoturret and AI support: The autoturret is a rapid-fire weapon equivalent
to an SMG, which works at an effective skill of 70% or the Rigger's SMG
skill, whichever is higher. Ammunition is 9mm, fire rate is effectively
3 bursts/round, each burst able to do 2d10 of damage, range of fire
extends nearly 360 degrees but does not cover the area directly behind
- Armor: Armor provides partial cover as well as protection for the bike--
assume 30% cover, i.e. if target is fired at (not aimed shots), there
is a 30% chance the bike armor protects the target (no damage)
The game system "Call of Cthulhu" and relevant concepts within are trademarks
of Chaosium Inc., and no copyright infringement is intended. References to
"Call of Cthulhu" game mechanics remain the property of Chaosium Inc.,
while the setting and background provided herein are concepts by this
author and do not represent an official Chaosium product.
Last modified February 3, 1997 by