A Way is a body of aether-patterns and words which are related to one another, and influence reality in a similar fashion. A Way spans a GURPS college. In accordance with the GURPS 4th editon rules for ritual magic (p. B), each Way is learned as a Mental/Very Hard skill.
Ymirean magic is divided into the following ways: Animal, Body Control, Communication & Empathy, Elemental: Air, Elemental: Earth, Elemental: Fire, Elemental Water, Enchantment, Gate, Healing, Illusion & Creation, Making & Breaking, Knowledge, Meta, Mind Control, Movement, Necromancy, Plant, Protection & Warning.
The GURPS colleges of Light and Darkness and Sound are subsumed under other colleges, mostly Illusion & Creation, the GURPS college of Food is subsumed under Illusion & Creation and Making & Breaking.
Individual spells are cast at a default ranging in most cases from -0 to -20. Each spell found in GURPS Magic and GURPS Grimoire functions as a Technique based on apppropriate Way skill. Hard spells are treated as Average techniques, Very Hard spells are treated as Hard Techniques. There is no minimum skill requirement for specializing in a spell as a maneuver.
To cast a spell, one needs both power and skill. Power is termed energy, in accordance with standard GURPS terminology, but might as well be called cratos, or authority
To cast a spell the sorcerer must
Every sorcerer has a basic skill with any spell with which he knows. This skill is used to determine both whether he is able to successfully cast the spell, and whether he is able to control it. These are inversely interrelated.
Casting skill is used to determine whether the sorcerer achieves what he wills – a successful roll means that the spell takes effect. A critical success causes the spell to succeed greatly. A critical failure means that the spell fails, and that a side effect takes place, even if the control roll is successful. This roll is made by the player.
Control skill is used to determine whether the sorcerer’s spellcasting unleashes any side effects. Such effects range from subtle to glaring, and from insignificant to catastrophic. The scope of such side effects are affected both by the degree by which the control roll was failed (or made, in the case of a critical failure at casting the spell).
A caster may choose to improve his casting skill by reducing his control, or to improve his control skill by reducing his casting skill. This is done at a ratio of 1:1 when increasing Casting skill, and at a 4:1 when increasing Control skill.
The ambient aetheranemos ("aether wind") may adjust the sorcerer’s skill. Greater movement in the aether, renders spells easier to cast, and harder to control, at an equal ratio. For instance, high wind in the aether gives a +2 to casting skill, and a –2 to control skill.
Energy. The ability to perform a task. The ability to change reality. . The stronger a sorcerer’s power, the greater his leeway with reality. Every sorcerer has an alottment of power, a capability for changing, which he cuts into whenever he casts a spell. To carve too deeply jeopardizes both his own well-being and the continuity of reality. By going out beyond his depth, he risks the uncontrolled ravages of chaos - calamities.
Spells do not automatically cause fatigue, rather, they count against a sorcerer’s Tally. Calculate a spell’s casting cost normally, and add that number to the sorcerer’s tally. Every dawn, the sorcerer’s tally goes down by his Recovery Rate (normally 8).
Each sorcerer has a Threshold (normally 30) which defines the maximal amount of energy that he can channel safely. When the sorcerer’s Tally exceeds his Threshold, he incurs the risk of a Calamity. Furthermore, he gradually comes to lose control over the energy that he is channelling, increasing the risk of a failed casting.
Every time the sorcerer casts a spell in excess of his Threshold, the GM makes a roll on the Calamity Table. This roll is modified by +1 per full 5 points by which the sorcerer exceeds his Threshold. For every 50 % by which the sorcerer exceeds his Threshold, he suffers a –1 to spellcasting skill.
Calamities range from personal inconvenience, all the way to global disaster.
Fatigue
To lessen his sorceries’ imact on reality, a sorcerer may attempt to take more of the strain onto his physical body, rather than in his soul.
Sorcerers may take fatigue to help power their spells, but it costs 4 fatigue to produce 1 point of spell energy. Energy gained from fatigue does not count against a sorcerer’s Tally.
Life Force
A sorcerer may also buffer his impact on reality through his life force. This is the thaumatological equivalent of putting one’s hand between the hammer and the anvil. To do so is both injurious and agonizing. Furthermore, the injury is done on both diffusely on the physical body, and on his ka, or astral body. Energy is gained from life force at a 1:1 ratio, one point of energy per hit expended. Energy gained from fatigue does not count against a sorcerer’s Tally. However, due to astral injury, the skill with the spell so powered is penalized by an equal amount. Furthermore, this penalty persists on all spellcasting until the injury is healed.
The Vitaphages are mages that specialize in fuelling their spell with life force, claiming that it is safer to do so than to jeopardize reality. They can draw on their inner life force with greater ease than normal sorcerers, and are even capable of fuelling their spells with other beings’ lifeforce, in folklore the sacrificial black lamb or virgin.
Reagents
Some organic objects have mana bound into them. This mana may be tapped by a sorcerer, and used to power spells, in essence, it functions as a one-shot powerstone. Such objects are known as reagents or "seidingar" (singular "seiding"). Some reagents come from beings that have mana bound up in parts of their body, so-called mana organs. Elven brains, as well as the hearts and tounges (and other body parts) of dragons are well-known mana organs. Another favoured reagent is the distilled mageblood, elfblood and dragon’s blood. Plants that grow in traditional sites of magic, or along aetherpotamoi, and such animals as may live there, often have enough mana residue to be functional reagents.
Another form of reagent is Magolith ("magestone"): Magolith is solidified magical energy, small (ranging in size from a blackcurrant to an apple, lighter than water) spheres that glow incandescent white. A magolith commonly holds powerful charge of mana (3d-2 spellcasting fatigue). Magoliths have a disturbing tendency to disappear with a flash (inflicting damage equal to its charge of energy, treat as a concussion grenade). This may happen if a magolith is touched by a living creature of greater size than itself, if it is brought into a aetherpotamos or if the aetheranemos in the area reaches gale strength or more. Thus, special spells or a lot of luck is required to tap its power.
With sufficient power, a sorcerer can do nearly anything. Many opinions are open to a caster effluent in power: