Dark Rules

Vessel

A vessel is a character’s total dark pool; once this value is depleted, a character can no longer cast spells. A character can never possess a dark value larger than her vessel. As a spell is cast, the cost of the spell is reduced from one’s vessel. Thankfully, vessel is the raw potential of dark and is a renewable resource, ever recharging. It can even be quickly replenished with specific concoctions. It is also entirely possible that vessel is not an inherent natural resource at all, and is something held in a physical container, either outside of the body or as an implant (see Dark Gear).
A starting vessel score is equal to half that character’s Vigor ability score (not modifier) + level. All characters with a Vigor score of 8 or higher gain access to vessel—it is not reserved by a specific class. As we will see later, a vessel’s value can be adjusted by background, feats, and archetypes. 
For example, a 1st level character with a Vigor score of 16 possesses a vessel of 9, while a 10th level character with a vigor score of 20 possesses a vessel of 20.

Vessel Regeneration (VP)

On your turn, you can regenerate your vessel. Select ONE of the following on your turn:

• Use a free action to regain 1 lost point from your vessel.
• Use a bonus action to regain 2 lost points to your vessel.
• Use an action to regain a number of points to your vessel equal to 1+ your Vigor modifier (this is your default VR score and can be modified by class features).

River

While asset and vessel represent constantly adjusting values, your river is relatively fixed. The river is your bank of quick-reference spells that can be called upon in an instant’s notice to be cast. The river is a simple value equal to your Vigor modifier—you can assign any spell into the river except for rituals.
For example, a character with a Vigor modifier of 16 can hold 3 spells in her river.

• Any spell with a casting time of one minute is reduced to an action while in the river.
• Any spell with a casting time of one action is reduced to a bonus action while in the river.
• Any spell with a casting time of one bonus action can be used once per turn as a free action while in the river. 

Anytime you finish a short or long rest, you can swap out any spells you possess in your river. Spells with a casting time longer than one minute cannot be placed in a character’s river. You are not required to put a prerequisite spell of a more powerful spell in the river to cast that more powerful spell from your river.

Commune

To commune means to communicate with another living individual you know in a non-vocal manner. You must have met the target physically at some point previously. As an action, you can establish a psychic connection with the target and communicate for up to a minute before requiring an additional check. 
The base DC is 10. 

• If the target is considered a friend, the DC decreases by 5
• if the target is a loved one or relative, the DC decreases by 10. 

Distance plays a factor.

• if you can see the target, the DC is unmodified.
• If the target is within 10 miles, the DC increases by 5
• if within 50 miles increases by 5 again. 
• Up to 100 miles, the DC reaches its ceiling, increasing by another 5; anything further requires a spell. 

You must share a language with the target, or the target must be able to understand you (like a trained pet). Once a connection is made, the target can communicate back (if they share a language) regardless if he or she is gifted in Vigor without making a check. The recipient knows who you are upon receiving the connection but cannot locate you.

Detection

Being endowed in Vigor allows you to be naturally receptive to its effects around you. This is similar to Perception except that it is narrowed to only detect fluctuation in the dark. You may ask, or a GM may request that you make a Vigor (Detection) check to analyze the level of dark around you. Depending on the difficulty of the task (set by the GM) you can attempt to detect the following within 30 feet of you:

• Natural regions strong in dark.
• Increased Vigor in living targets (those with an ability score of higher than 12).
• Artifacts or mechanisms either bottling the resource or otherwise strong in dark. 
• Messages between individuals employing the Commune skill.

This ability can penetrate most barriers but is blocked by 1 foot of stone, 1 inch of common metal, a thin sheet of lead, or 3 feet of wood or dirt. Contrary to popular conspiracy theory, aluminum foil alone will not suffice.

Induce

There are those able to push their inbuilt magic beyond its limitations. This is known as inducing. Many magic effects provide an option to boost via a Vigor (Induce) check. However, after a check is made, the target suffers damage equal to the final roll result OR the DC of the check – 10 (whichever is lower). If you fail at the check, the base spell still goes off as indicated.
For example, if a character is attempting a DC 20 Vigor (Induce) check and rolls an 8, that character suffers 8 damage; if the character rolls a 25 (succeeding at the check), that character still suffers 10 damage.

Natural Results

If a character rolls a natural 1 on a Vigor (Induce) check, it is an automatic failure, and the target is stunned until the end of the character’s next turn. If the character rolls a natural 20 on a Vigor (Induce) check, it is an automatic success, and the target suffers no damage from having made the check.