System

The Basics:
Cortex is a step-dice system; this means that traits are rated d4, d6, d8, d10, d12
d4 mean that the trait is a bit weak or problematic; d6 is about average, d8 is a great trait, d10 is superb, and d12 is mythic

Whenever you roll to take an action, you assemble a pool of dice made up of whatever traits you have that are relevant to what you intend to do. You can add in one trait from each category, e.g. an attribute, an ability (skill), an aspect, a birthright, a boon/knack, a virtue, scene aspects, and stress (although it is unlikely that you will have something from every category that is relevant to the task at hand).

Roll your assembled dice, and hope for high numbers. Put any dice that come up 1 to the side; I’ll come back to those in a bit.
Now pick two dice to add together for a total (the higher the total the better, so your are normally going to want to pick the two dice that rolled the highest number and add them together).

If the total of your chosen two dice beats that you your opponent (usually the GM), then you win.
If the outcome of the roll changes something (which it usually will, such as creating a scense aspect or inflicting stress on an opponent), then you pick a third die as your effect die. The number that was rolled on the effect die doesn’t matter, just its size (e.g. d6, d8, d10 etc). For example, if you succeed on a hacking roll then you may use you effect die to create an aspect like “Compromised Security, d8”. Aspects like this will generally hang around until someone uses them in a roll, and then they go away (however, you can spend a legend point to make the aspect persistent, meaning the you can use it on multiple rolls and that it won’t go away until someone successfully rolls to remove it).

Now, remember those dice that rolled 1? Those are potential complications/botches/glitches (opportunities for the GM). The GM can give you a legend point to take advantage of those 1’s, either by describing something bad happening to you and/or by increasing the doom pool (which means storing the trouble up for a latter time). The more 1’s you roll, the more complicated and problematic things will be for you.

Of course, the GM sometimes rolls 1’s as well. When this happens, you can spend a legend point to activate a complication for the NPCs, or for a bonus on your next roll (see below).

Stress:
Stress is how the game deals with the negative consequences of conflict (i.e. damage). Stress comes in 3 flavours: physical (such as injury and exhaustion), mental (such as confusion and mental fatigue), emotional (such as anger, fear, and embarrassment).

Stress goes 0, d4, d6, d8, d10, d12, stressed out. D4 stress is very mild, such as having a few bruises, being a bit rattled, or being slightly frustrated. D12 on the other hand is serious stuff such as being beaten up to the point where you can hardly stand, totally zoned out, almost paralysed by fear or confusion, becoming lost in rage or misery etc.

When you taken a new die of stress, compare it to your current stress rating in that category; if the new die is higher it replaces the old rating, and it the new die is less than or equal to the current rating then you step up the rating by one.

Opponents can use your stress against you in their rolls (e.g. if you have d8 physical stress then they can add that d8 into their dice pool when fighting you, to represent them taking advantage of your injuries).

Stress steps down by one during any scene where you are able to rest and recover. On top of that, you can roll to recover faster if you are able to properly rest and tend to your stress. If the effect die from your successful recovery roll is greater then the stress die, then you wipe off your stress; if it is equal or less, then you step the stress down by one.

When your stress goes over d12, you are “stressed out” of the conflict (i.e. defeated). When this happens, you also gain d6 trauma (unless your enemy chooses to pull their punches). Stressed out characters loose all of their stress at the end of the scene, but keep their trauma.

Trauma is similar to stress but is much more long-lasting and difficult to recover from. Trauma covers things like broken bones and serious wounds, severe phobias, and crippling depression. If your enemy is able to continue attacking you after you have stressed out of a scene (usually only done by bitter or sadistic enemies), then they can increase the trauma that you have taken. If a character takes over d12 trauma, they are dead (or similarly removed from the story).

Like stress, you opponents can add your trauma into their dice pools; however, they can only add one or the other – they can’t add both your stress and trauma without spending legend/doom points.
Trauma is much more difficult to recover from then stress – it requires much longer time-frames. Trauma steps back by one automatically at the start of a new story or act. You can also make a recovery roll against trauma (given the time and resources, such as a few days in hospital). When you make a successful recover roll against trauma, if the effect die is higher then the trauma steps back by one, if the effect die is lower then the situation remains stable; if you fail on the trauma roll, then the trauma will actually step up by one (representing a complication).

House Rule: at any time your can exchange your stress for a trauma die two steps lower (minimum d6). This will help to keep you in the fight, in exchange for more significant injuries in the longer term. In addition, this earns you a legend point.

You can actually take advantage of your own stress, adding in into your own dice pool (e.g. using your own anger and fury to make your attacks more powerful), but it has the negative consequence of automatically stepping up that stress die by one afterwards. Adding in stress in this way usually requires the expenditure of a point of legend.

Loosing a conflict:
When a character is stressed out of a conflict, their opponent narrates what happens to them, within reason. When you choose to concede a conflict, you instead get to describe how you are defeated on your own terms (occasionally a legend point may change hands to facilitate this, depending on the situation). Points of legend flow freely in these dramatic situations: you will often earn legend points for when you loose a fight, based on roleplay and how much stress you took (as a general rule you will earn a point of legend for d8 stress, two points for d10 and three points for d12).

Legend:
You start with 4 points of Legend; think of them as Plot/Fate/Edge Points. You can spend legend to gain all kinds of benefits:

Make a declaration: you can say something like “my character finds a length of pipe in the alleyway that can be used as a weapon” or “I have contacts in the Mafia”, and if the GM is OK with it you spend a of legend and it becomes true.
Add a d6: add a d6 to your pool to represent an advantage or detail that you describe (if you describe it in a cool way this dice will be stepped up to a d8 or even a d10 for no extra cost)
Add an additional trait from the same category: in some situations you may feel that two of your attributes or abilities etc are relevant at once (e.g. both strength and dexterity); in these situations you can pay a couple of legend points to include the second trait from the same category in the roll (I may drop the cost down to 1 point if the justification is very good).
Activate a power: some powers (boons & knacks etc) require a point of legend to activate
Add an extra die to your total from your roll: count another die into your total, so you add together 3 rather than 2 dice (or 4, if you spend a second point of legend)
Keep and extra effect die: this is how you do two things at once in the game, such as shooting someone whilst uttering a spell. Spend a second point a legend and you can keep another effect die, allowing you to do three things at once, etc.
Use an effect die from a reaction roll: normally when you are making a defensive roll then the outcome when you succeed is simply that you avoid what would have happened to you (e.g. you doge the sword thrust, or see through a lie). However, if you spend a legend point you can actually have things happen to your benefit, such as not only dodging the sword thrust, but overbalancing your foe and creating an opening to take advantage of.
Make an aspect persistent: normally any aspect you create will be available of you to use only in one roll. However, by spending a plot point you can make it last for the whole scene (or until something happens which removes it).
Activate a 1 rolled by the GM: when the GM rolls a 1, you can spend a plot point to step up one of the dice in your pool to represent a complication for the NPCs or and opportunity for you.
Change the type of stress you take: e.g. when you take physical damage you could spend a plot point to explain how it impacts you emotionally instead (e.g. the punch doesn’t connect as a knock-out blow, but instead into knocks your pride an confidence.

You earn Legend points from using your aspects at d4, from having the GM activate any 1’s that you roll, from doing epic deeds, and from good role-play.

The Doom Pool: (this is something only the GM has to worry about, so you don’t need to read it)
The doom pool seems to reset between acts (not scenes, but acts). It starts at 2d6 by default, but can be as much as 4d10.
When the players roll 1’s you can give them a legend point to add a d6 to the doom pool. You can also step up dice in the doom pool by one step for any additional 1’s rolled (this does not usually require the PCs to earn legend points).
NPCs can use their effect die from an action to directly add to the doom pool (by making things indirectly hard for the the PCs, or by causing general mayhem etc).

The doom pool dice an be directly added to the pool of an NPC (usually only one die, but nothing says you can’t use this for more than 1 die at once). The doom dice disappears after the roll; however, you can give affected players a legend point and instead return the die back to the doom pool.

The doom pool can also be used to count additional dice towards the total, but spending a doom die equal to or larger then the size of the die that you wish to add.

Similarly, you can keep an extra effect die by spending a doom die of at least that size.

You can spend a doom die of any size to keep an effect die on a reaction roll.

The GM can directly use a doom die to create a new scene distinction (aspect), usually a d8 (e.g. d8 burning hallway). Alternatively you can add in a scene distinction at d4 that helps the PCs and hinders the villains, in which case you step up the lowest die in the doom pool instead of spending a doom die (this is how distinctions work of NPCs as well).

Doom dice can be used to interrupt initiative (basic cost of d6, but may need to spend more to overcome PCs with high dexterity or wits).

Any time that the PCs are making a roll that is not opposed by any NPCs, the doom pool acts as generic opposition. When this happens, pick up a pool that matches the doom pool (we roll a clone doom pool to avoid confusion with what dice to put back into the doom pool later) and add in a couple of dice for the scene to represent any objects of difficulties etc).

Every time the watcher spends a d12 from the doom pool all affected players can either a plot point or an experience point (as chosen by the GM).

System

Scions of the Old Gods seidgaldr