The ability to create custom spells is one of the most powerful perks acquired by joining the Mages Guild. However, it is also available to those who have the Frostcrag Spire plug-in, after purchasing the Magetallow Candles altar upgrade. The spell cost is determined by the equation below: B = Base Cost / 10 M = Magnitude ^ 1.28 D = Duration A = Area × 0.15 Total cost = B × M × D × A If M, D, or A is less than 1, a value of 1 should be used. The Magicka cost is further multiplied by 1.5 if the spell is a targeted spell. Base Cost is as defined in the construction set. 1.4 - 0.012 × Skill