Will

Your Will represents your mental fortitude, the hit points of your soul. Depending on how you build your character, Will might be a resource, a hindrance, or an afterthought. In many ways you can see it as an invisible analogue of Health, but the ways in which you can use and lose Will differ greatly.

Losing Will

While your Health depletes as a result of taking damage to your body, your Will depletes as a result of taking damage to your mind. If you are a character whose specialties lie in their charm or intellect rather than their physique, you may find yourself suffering more Will than Health damage: trying to exert your authority over someone and failing, as an example, will harm your self confidence and state of mind. Or, using ancient technology may lead you to perceive truths you are not meant to know, straining your perception of reality itself. Most causes of Will loss are:

--Attempting a CHA or INT-based Skill check (except Barter and Animalia) and failing. Regular failures typically cause 1d4 Will damage, while critical failures double this.
--Trying to use or understand ancient or bizarre technology or concepts.
--Being subjected to attacks that target your Will.
--Failed Psyche saves (sometimes related to the above).

In cases of failed rolls, the amount you failed by determines Will damage: failures by 1-2 equals 1d2 damage; by 3-4 equals 1d4 damage, and so on. Will attacks and failed Psyche saves will have a set Will damage roll attached, so you might face a Will attack that does 3d6 damage and roll a Psyche save to prevent it. If you hit 0 Will, you fall unconscious and on each of your turns you must make a Collapse saving throw. Roll a d20; on a 2-9 you fail, and on a 10-19 you succeed. Three successes stabilises you and returns you to 1 Will, while three failures renders you permanently catatonic and for all intents and purposes dead. A roll of a 1 is equal to two failures, while a 20 is equal to two successes. Just like when you are dying, an ally can use their standard action to stabilise you.

Note that only intelligent people and creatures have strong negative effects from losing Will and suffer collapse: animals will just run away as fast as they can at 0 Will.

Using Will

You can also abuse your mental health for profit. This comes in the form of Interfacing with esoteric devices - from invisibility cloaks to energy weapons - as well as various abilities you can gain through gameplay or Perks. These will have a specific, flat cost to use balanced by unique benefits.

Regaining Will

You regain up to half of your maximum Will at the end of each Long Rest. Certain abilities and items can also restore lost Will, though usually in smaller total amounts determined by dice rolls. When you level up, you immediately regain all lost Will.