Spellpower

Spellpower is the Mage's critical secondary attribute, and is equal to 10 less than the caster's Magic attribute (with a minimum of zero). It affects the effectiveness of all spells and Shapeshifting forms of the Mage. Spellpower is not calculated for Rogues or Warriors (their skills use a similar construct, e.g. many Rogue abilities are affected by Cunning-10).

Mechanics
Mages benefit from spellpower directly and indirectly: spellpower increases the magnitude & duration of spells and also helps overcome the mental or physical resistance of those affected. As a rule of thumb, most spells increase impact by about three to six points for every ten points of spellpower, although some follow a different formula. There are also a few spells unaffected by it.

Common Formulas

 * Formulas only determine a spell's raw potential; they do not take into account mitigating factors on the target or enhancing factors on the caster.
 * Mitigating factors include: damage types, resistances, magical shields, game difficulty, relative ranks
 * Enhancing factors include caster level and spellpower's ability to overcome resistance(s).

Boosting Spellpower
Spellpower can also be enhanced above its base through the use of spells or wearing items.

Skill/Spell Boosts

 * Spell boosts: two spells increase power by a fixed amount (which itself is based on spellpower):
 * Spell Wisp adds 5 + 0.05*[Spellpower] points
 * Spell Might adds 10 + 0.1*[Spellpower] points (i.e. twice that of Wisp)
 * Ability boosts: Arcane Mastery adds 5 to spellpower (the same impact as increasing the Magic attribute by 5)

Example
Mage with spellpower=100 casting Heal
 * Base healing: 40 = (100 + 0) *0.4
 * Add Spell Wisp: 44 = (100 + 10) *0.4, ← Wisp adds 10 = 5 + 100 *0.05
 * Add Spell Might: 48 = (100 + 20) *0.4, ← Might adds 20 = 10 + 100 *0.1
 * Add both: 52.4 = (100 + 31) *0.4 ← Might adds 21 = 10 + (100+10) *0.1 ← Wisp adds 10 = 5 + 100 *0.05

Item Boosts
A number of items also enhance spellpower, notably a variety of staves, amulets, and rings.