Mana is the fluid form of Prime, the prima materia, Supernal energy filtered down into the Fallen World. Some of it is residual energy left trapped when the Abyss formed, recycled over the millennia into a thousand forms, but some of it is fresh, brought into the world by a mysterious form of grace from on high.
Mana is an Advantage trait for mages. A mage can hold up to 10 points of Mana in his Pattern, and he can hold even more with increasing dots of Gnosis.
Mana itself is normally invisible and intangible, undetectable to those without Mage Sight. Any mage standing in a Hallow can sense its ambient Mana with a successful Wits + Occult roll. Mages perceive Mana in many different ways. It is most often described as a fiery, fluid energy, either pure white or prismatic, containing all the colors of the spectrum. Some mages perceive Mana as another sort of power or force, in accordance with their own Path. The particular Arcanum a mage uses for his Mage Sight often colors the experience.
Improvised Magic - Casting an Improvised spell requires the expenditure of a point of Mana, unless the primary arcanum used is one of the Mage's Path Arcana
Sympathetic Spells - Casting a spell upon a target beyond sensory range requires the expenditure of a point of Mana
Aggravated Damage - Mages must spend a point of Mana for a spell to inflict aggravated damage. The mage must fist have the prerequisite Arcana dots to cast and aggravated effect, as described in the spell descriptions.
Pattern Restoration - Mages can infuse Mana into their physical Patterns to heal wounds. The cost is three Mana points per one Bashing or Lethal wound. This is an Instant action. Mages unable to spend more than three Mana per turn can take as many consecutive turns performing this action as they need, until they've spent all three points. Pattern Restoration cannot be used to heal Resistant damage.
Paradox Mitigation - Mana can be spent on a one-for-one basis (up to the maximum allowed per turn according to the mage's Gnosis) to reduce the dice pool for Paradox, to a minimum of zero dice (or a chance die).
Mages can scour their own Patterns to free up Mana. A mage elects to degrade one of his Physical Attributes by one dot in return for three Mana points. The lost Attribute dot is restored one day (24 hours) later. He might burn muscle mass (Strength), transform nerve impulses (Dexterity), or convert adrenaline (Stamina). It takes a full turn to perform a Pattern scouring, during which time the mage can do nothing but move his Speed.