Magic residue is the physical representation of manipulation of magic. When the lattice is bent, altered and broken, clouds of power fragments (or "residue") permeates the local timespace area, fly in and out of our reality, gets stuck to objects and clothes that were in the vicinity of the spell's casting and can be detected by skilled mages. This works similarly to how a dog's scent can detect smell particles in the physical world.
Active enchanted items, spells, powerful creatures as well as traces from previously cast spells can be detected in this manner.
The magic residue rules replace magic auras from the D20 SRD rules.
Detect Magic is the most commonly used spell when finding residue using the Spellcraft skill (any similar spell is referred to as Detect Magic here). With enough aptitude a caster can not only detect magic residue of previously cast spells but even figure out which spell was cast. In the case of active spells, enchanted items and magical creatures, they also expel residue by their mere existence, which can be noted in the same way as residue left by already cast spells.
Residue is measured in twinkles and is calculated differently depending on the source of the residue. Auras from the magical fragments are easier to detect the more twinkles constitutes remaining power (see Table 1:3 Magical Residue).
All residue has a Half-life Period depending on the original source. Any given amount of residue from this amount of residual twinkles will half once every halflife period, indefinitely. (see Table 1:2 Residue & Halflife Periods or use a calculator) Of course, more particles can accumulate, with their own halflife periods.
When detecting individual magical auras with Detect Magic, the caster automatically realise that it is in fact residue (as oppoed to an actibe power source) and roughly how many Twinkles of power it is (GM's estimate). A Spellcraft check can also give a rough estimate of the original spell's power and the time since casting.
The amount of twinkles in the residue originally created is calculated as slvl x clvl. This number is in turn halved in a number of minutes equal to slvl x clvl. (see Table 1:2 Residue & Halflife Periods or use a calculator)
The more total twinkles of residue that is available at time of detection, the easier the residue is to detect and identify (see Table 1:3 Magical Residue); multiple spells stack for the purpose to detect ANY magic residue, but not to attempt to detect which individual spell was used. Note that DC's lower than 1 can still theoretically be failed with natural rolls of 1 or 2 as per the modified Spellcraft skill, or if the DC is raised in other ways.
Example: Exarch the 9th level wizard disposes of several of his enemies in an ambush with a Cone of Cold on the Green Hill north of Scima. When summoning arcane powers and channelling them into the destructive force of the Cone of Cold he leaves behind residue of no less than 45 twinkles of power (worth about 1.5 spell slot). Even a very incompetent caster would have a hard time failing to notice this Moderate residue aura at a Spell Craft DC of -2!
When Exarch leaves the area with his allies, the residue will naturally dissipate. 45 minues after casting there will be 22.5 twinkles of power left (Faint aura of DC 3) and in another 45 minutes after that only 11.25 (Faint aura of DC 12). Another 1.5 hour later only very skilled casters would be able to detect the traces of the spell (Dim aura of DC 21) and in 1.5 hours after that it requires one of the most powerful casters in the world (Trace aura of DC 33).
- Note: In the example above, DCs are displayed whereas a PC would only be told if the aura was "Moderate", "Faint", "Dim" or "Traces" by the GM. It's most likely an investigating caster wouldn't even be able to see the Trace aura.
NOT DONE HERE!!!
Multiple casts of spells increase the total amount of power in the area and decreases the difficulty to detect magic activity but it doesn't help detecting which individual spells were cast, but a natural roll of 1 or 2 will still mean the detection fails.
- Magic Items
Destroyed Magic Items
A destroyed magic item will spread a large amount of magic power. Do Spell level times caster level for each spell used in making the item, add them all together, divide by two and the final number is counted in Sparks instead of Twinkles ((slvl x clvl) + (slvl x clvl) + (slvl x clvl) + (...)) /2 = Sparks. The aura is easily recognised as a destroyed magical item, though no longer possible to determine its school.
A skilled caster can not only detect magic residue, but even figure out which spell was cast. Portions of the spell also lingers, and it's entirely possible to attempt to absorb residue to either hide that a spell was cast (or a magic item destroyed). If enough of residue is absorbed, the power can be reused as sparks (but more likely twinkles).
A caster locates the aura of the cast spell but will notice it is not a currently live spell as soon as she knows how many auras are present. She can also use Spellcraft to get a rough idea of how many twinkles of power is residual. A Spellcraft check can also give a rough estimate of the original spell's power and the time since casting.
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