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In many settings there are light and dark versions of powers. Dark force and light force in Star Wars, Defilers and Preservers in Dark Sun and so on.

In this post I will use the term dark power for powers that are generally more evil (could be subjective) but could be more powerful and light power for the good version. Ability would be something fueled by the power and you could use either dark or light. Generally players would be light power users that might be tempted by the dark usage.

I was wondering if there were any interesting mechanics out there that fulfill my criteria or if anyone would come up with something. I'm not currently planning on using any of this at the moment but I've been thinking about this for some time.

To make this less open ended I would pick the answer that I would use as a model for a game that centers around this, even if that meant using a specific system.


  • Using the dark version should be rewarding in some way, probably more power to the ability in question.
  • Using the dark version should also have the possibility (either certain or a chance) of some bad side effect. This effect may be long term, delayed or generally not relevant at the time of the ability's use.
  • While the players are generally light power users, they should be able and tempted to use the dark power when in dire need, so they have to make a choice.
  • Using the dark power shouldn't doom characters and they should be able to not be totally screwed if they use the dark power once or within limits.
  • There should be a degree of uncertainty to using the dark power so players can't know beforehand how badly they could screw themselves ("I'm okay using the force choke because I'm still 3 points from something bad" would make it too predictable).
  • Bonus points if it models the slippery slope of darkness, and if it increases the likelihood of bad side effects the more the dark powers are used.
  • A complete fall (going over to the dark side) isn't necessary but a nice feature to have.
  • And of course should be interesting to role play and generally fun (subjective I guess).

The rules can be generic or system specific (i.e. using compels in Fate or Beliefs in Burning Wheel to some effect) and can be described as such. Using numerical modifiers is okay to show relative bonuses and such, and examples are encouraged.

If you mention system specific mechanics it would be great to mention a little bit on how they work.

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Since you specifically mentioned beliefs in BW: if you have the books handy, take a look at emotional attributes in BW, especially Grief and Greed (from the core book), Corruption (from Magic Burner), Spite (from the freebie Dark Elves supplement), and Shame (from The Blossoms are Falling). –  Alex P Jul 30 '12 at 14:13
@AlexP I don't know much about BW, but I've read the interesting one shot adventures like The Gift which especially mentions Greed and Grief. I was always intrigued by how the system would handle these as they sounded to be both advantageous but also disadvantageous at the same time. –  Ingó Vals Aug 2 '12 at 18:41
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6 Answers

My group ran a fairly successful corruption system in the D6 Star Wars RPG. It was cobbled together from the core rules, and the rules laid out in The Jedi Handbook v1.3.

To help give a sense of scale, here's the core mechanics of the system we were using:

Players have skills and attributes rated as a number of dice (i.e. 3D). To use one, roll a number of six-sided dice equal to the rating of the skill and total them.

One die is always a different color from the rest. If it shows a one, remove it and the highest other die from the roll. If it shows a six, it explodes and is rerolled until it doesn't show a six (adding to the result each time).

Player characters typically have skills in the 2D to 6D range.

Character points are a type of experience/meta-point hybrid (lose one to add a die to a roll). Force points are large meta-points (use one to double all rolls for a turn).

Our Dark Side Rules

Whenever a character commits a dark side action, they receive a Dark Side Point (DSP). Some Force powers automatically award DSPs, other actions are up to GM discretion (players are usually warned).

When a character reaches six DSPs, they turn to the Dark Side and become an NPC.

Players with DSPs may choose to feed on them, and add bonus dice to their Force powers equal to the number of DSPs they currently have. If they do so, they are much more at risk of gaining DSPs from the Force use (i.e. using an attack power directly will likely now result in an additional DSP).

If players do not wish to feed on the DSPs, they must fight them. This increases the difficulty to use any Force power by one level (approximately five to ten points).

Whenever a character with Dark Side Points is in a position where he may commit evil, the GM rolls a d6 and if that number is less than or equal to the number of Dark Side Points then the Dark Side demands some action for the Jedi to perform (note: the D6 is wild, thus a roll of one is "less than" one DSP).

When a character has 1 to 3 Dark Side Points, they are tempted to commit actions that involve the immediate situation. For example, if an enemy was subdued, the Jedi fighting him may be tempted to kill the villain, even though he has surrendered.

To resist this temptation, a Force Sensitive character must make an opposed roll of Willpower, or Perception, vs. the GM's roll of one die for each Dark Side Point the character possesses. Non-Force Sensitives add their Willpower and PER die codes together(with only one wild die) for their roll to resist, since they are not affected by the Dark Side as much.

When the character has 4 or 5 Dark Side Points, their temptations turn to causing unnecessary harm and destruction, or initiating unprovoked attacks. The character is still entitled to a Willpower/Perception opposed roll, as above. If they succeed in the roll, then they may act normally, but the Dark Side enacts a punishment, according to the following table.

PC rolls >
GM roll by  Character Loses
 0 - 5       1 Force Point (or Character Point's equal to # of Dark Side Points x3)
 6 - 10      Character points equal to # of Dark Side Points x2
11 - 15      Character points equal to # of Dark Side Points
  16+        Character points equal to # of Dark Side Points x.5 (rounded up)

If the character is unable to pay off the cost he must “take” 1D from the attribute or Force Skill of his choice. Naturally, all skills based on that attribute will be reduced also. If any attribute ever reaches 0D, the character is consumed by the Dark Side and dies.


When you have 1-5 DSP you may begin to atone the cleansing of the corrupting influence of the DS is a long & difficult process & you must be of serious mind while attempting to atone (GM discretion). You must choose your way of atoning based on spiritual belief. (the Jedi usually fast, reflect through ritual & meditation & renew their commitment to live by the Jedi Code & the ways of the Light). When atoning you must actively work against evil from occurring, & follow a base code in creating your personal spiritual atonement process, with the following guidelines:

Reaching each through non-violent solutions when possible

  1. Preserve the existence of Life
  2. Preserve the rite to gain knowledge & enlightenment
  3. Preserve the rite of peace & harmony
  4. Defend the defenseless

Time required: of approximate atonement, all atonement must begin again if a DSP is received during atonement. Increase time required for characters who have removed DSPs through atonement in the past.

1 DSP = 40 days
2 DSP = 60 days
3 DSP = 80 days
4 DSP = 100 days
5 DSP = 120 days

These rules worked out pretty well... There was always the temptation to get just one or two DSPs in exchange for doing something evil but expedient. But thanks to the wild die mechanic, even a small number of DSPs could occasionally spiral wildly out of control.

Likewise, players who were corrupted had to choose between more power, at the cost of an increased chance of more corruption and the inability to atone, or more difficulty using their powers.

Case Study: Marcus Orion

The most successful use of this system was a Jedi character named Marcus Orion. The system played out like this:

  1. Marcus received one DSP as a result of sacrificing himself to save others, then being captured and trained by a dark jedi.

  2. Marcus managed the first DSP, but quickly received a second one by using it to fuel a particularly deadly attack power.

  3. From two, Marcus spiraled upwards to three and four by failing temptation rolls. This reset his atonement timer each time.

  4. At four, Marcus finally had enough invested in Willpower that he could resist the temptation rolls. With some careful management to minimize opportunities for rolls, he was finally able to fully recover.

This entire process played out over the course of several real-time months, and felt like a truly epic addition to that campaign.

Adapting to your Game

In your case, you would probably move away from the fiat-based moral judgement, and attribute DSPs directly to using the "dark" version of the various powers.

Because the granularity of the system is low, I would recommend either increasing the number of DSPs (and reducing the individual effect of each one) prior to turning, or allow the players a roll to avoid receiving one when activating a dark power. Tune based on how quickly you want a dark user to become corrupt.

Alternatively, you could scale the roll to have a lower impact on corrupt characters, i.e.:

  • No DSPs -- Automatically receive a DSP.
  • 1-3 DSPs -- Difficult roll to avoid receiving a DSP.
  • 4 DSPs -- Easy roll to avoid receiving a DSP.
  • 5 DSPs -- Trivial roll to avoid receiving a DSP.
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Ravenloft for (A)DnD is an excellent choice for the exploration of evil roles (in a gothic horror / fantasy setting, by default.)

What you get with it is a rules expansion for (A)DnD that allows you to measure - in a pretty unobtrusive way - game effects like fear and horror (that the characters experience), and that also presents you with a multi-level, gradual system to track and measure the evildoer's descent into madness, inhumanity and corresponding, symbolic, physical mutation. This systems also presents incentives for the evildoer, trying to "lure" the character deeper and deeper with rewards that partially compensate them for their degeneration.

As for the world of the setting: Officially it consists of "domains" that map 1) the most famous literary pieces of the gothic horror genre and 2) samples of DnD's most famous settings into a relatively(!) consistent whole. However, due to the nature of this setting - the "domains" being separated by "The Mists", a secret, godlike power(?) -, it is extremely easy to bring anything of your own design under Ravenloft's rules.

Personally, I'd recommend the version published for DnD3.5, but most other editions are great as well. (In fact, the earlier the books, the better they look. Poor 3.5 version is full of pretty weak illustrations that can be a great turn off for a certain kind of people... like me, for example. I do owe the previous editions though, and can fall back to those when in need of visual inspiration, relying on 3.5 for rules only.)

Note, please, that Ravenloft, by default, does not encourage playing evil characters. PCs are supposed to be heroes tempted by evil and resisting it to the best of their abilities. However, the rules hinted at above provide a solid yet simple system that could meet the requirements of the Q.


PS: In case you're not into (A)DnD, you might want to take a look at Kult, which, though an old game (that definitely belongs to the horror genre, so reader discretion is advised, again), also has a rather efficient system for the measurement of characters' mental balance (+/- extremes) and corresponding mental/physical changes. Kult, by default, is set in a relatively contemporary setting - however, it features dream realms in which a whole isolated fantasy campaing could easily be set up.

Never done this before, but this is entirely (99.9%) a quote, of my own answer given to the question "What fantasy systems center on evil characters and specifically the consequences of being evil?" (that you may want to check out for it is quite similar to yours.)

Ravenloft's Dark Powers Checks system meets most if not all of your criteria.

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World of Darkness uses the Humanity stat for something very similar to this in Vampire: the Requiem.

In brief, all vampires have a Humanity score that ranges from zero to ten, and which is affected by a variety of game events. Doing "bad" things generally incurs a chance to lower your Humanity score, though you have a chance to roll to avoid losing Humanity. "Bad" things include relatively common events like feeding off of a human's blood, and breaking powerful taboo like "diablerie" (consuming another vampire's heart blood in order to absorb their power). Note that the things which lower your Humanity are things which players want to do, either because it's periodically required by game mechanics, or because it offers the greatest chance at advancement.

Game mechanics generally reward having a high Humanity score. Any social interactions with humans involve a Humanity success roll, and a number of skills have a Humanity component to their success rolls. Characters with a Humanity below 2 suffer significant penalties, and if your Humanity drops to 0 your vampire becomes a draugr (a mindless hunting animal, which is generally put to death by other vampires because of the dangers it poses). This effectively means that you've lost and don't get to play any more.

This creates an interesting tension for players between immediate rewards and long-term rewards. Long-term, having a high Humanity score is generally advantageous, but maintaining that score is very difficult, especially as a vampire ages. Taking actions that can lower your Humanity is often easier and more appealing, but if you continually do them you may handicap yourself in the long run, and you run the risk of losing control of your character altogether.

More detailed information can be found in the Vampire: the Requiem sourcebook.

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I've got a number of approaches to going slowly to the dark side; some of them work more like what you asked than others, but here you go:

  • Require the character to "breach" their ego to reach the wonderful dark side powers of fun and doom. They will gradually get better at it, but once they go too far the stuff on the other side of the curtain can freely take control of them. This doesn't have to be irredeemable, but it does allow them to lose control if they use the super duper (demonic/Lovecraftian/Warp/magic/evil) power too much. The way I would handle this mechanically is basically to give the character an appropriately named percentile rating, and whenever they have major stress they have to roll at -20 on it to prevent automatically using their dark powers and going a little over-the-top. Bonus points if the horribleness is stigmatized in society.
  • Another, similar system works on a point-bid where players have to buy their dark powers at the cost of various things, slowly lowering their other stats to create more power. However, when dark powers are used, they can temporarily regain these points, relative to the power of what they do, but then they may be forced to delegate more points of otherwise normal stuff to operate in this way. This works by providing a temptation for those who have already built up a substantial power base, but not so much for light side users.
  • Another thing you could do is just to make a dark-side analogue to everything; it's quicker, cheaper, and more powerful, so it's definitely tempting, but it is balanced out by long-term psychological damage (CoC-style SAN works well for this), as well as social stigma. In addition, dark powers could have a chance of backfiring if they prove too popular, though this is far from necessary.

And now that I'm back from work I'll add on a second list of things that I've been thinking about as well.

  • Make stuff that builds dark side affinity have greater rewards. I don't know if you've ever played Knights of the Old Republic, but you would get dark side points for certain actions, but if you wanted to be rolling in dough you could take advantage of those around you and get a quick fix. Basically, things that grant incredible expediency at the cost of major damage to others could give a few dark side points.
  • Dark methods could be the only way to get certain things; think blood magic or the like that is obviously evil (well, when performed on others), but if you want someone else to provide the power for your spells, it's pretty much the only way to do it on the fly. Similarly, it could be that the players could use themselves, but would be tempted to use others (Earthdawn has blood magic that you can use with your own blood; bloodpebble armor coming to mind, but you could also use others' for pretty good results without draining your hit points away).
  • Dark powers could have a point of no return based on random chance-some people can use dark magic hundreds of times and not have issues, while some people just have no luck and are possessed by gremlins the first time they cast. This puts in arbitrary penalties, but can make things interesting. If you want to curve it, it'd be pretty easy to weight the roll based on times used, though this is pretty similar to my first.
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Note: This post is about something called the Dark Powers; when capitalized like that, it refers to them. When lower-case, i.e. "dark powers", it refers to the evil abilities in the question.

The Ravenloft setting for AD&D had something called Dark Powers checks: whenever someone did something evil, the Dark Powers had a chance to notice them; the more evil the act, the higher the chance. If the Dark Powers did notice you, you would progress down a track.

In some versions, progression initially gives minor benefits, as the Dark Powers try to lure you into progressing further. The middle range gives larger benefits but also penalties, and the later steps only give penalties (since at that point it's almost impossible to turn back), and at the end of the track the character becomes a super-villain (and an NPC, if they weren't already).

You could give all your dark powers a buff in potency, but also have them require a Dark Powers check.

One version of the Dark Powers check rules can be found here (it spans several pages). This version has benefits & penalties at every stage; the strength of the benefits & the severity of the penalties both increase as you progress down the track. Note that the minor, moderate, & major changes listed are only suggestions: you can (and should) come up with custom changes of approximately the same power level that are specifically tailored for the character to suit the kinds of evil deeds they're doing.

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Primarily I am agreeing with Ace. However, I thought an example of what I did in another game might also provide some insight and long enough to be its own answer.

In a game of Scion, I was delving into power at the cost of corruption using a homebrew rule. Each character was given the ability to reroll any roll "for free". behind the screen I had replaced their lowest of four virtues with a one point "virtue" from the four that they give monsters. Each time they used the additional reroll, I kept a tally. After the first two uses, whenever a roll fell short that I could tell that given player really wanted to succeed, they started needing to roll Willpower, needing a better roll for more of the new stockpiled Virtue.

So one thing you could do is start having the characters make Willpower rolls needing a higher threshold for every DSP they have. Failure makes them use the "dark power" compulsively and take all of the associated risks/penalties involved.

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This doesn't really make them tempting, just surprise-compulsory. –  SevenSidedDie Jul 30 '12 at 22:56
True, but my table was pretty sharp and caught on quick to the fact that they were being groomed to take on possessed artifacts, and the first time any of them was forced to do a reroll they started scaling back on the extra power. –  CatLord Jul 31 '12 at 3:23
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