Sorcery and Certain Psyker Effects
Though greatly frowned upon by the Imperium, it is possible for an Explorer to come across ancient tomes, ruins, or teachers that know the ways of the Warp. And because of this, it is entirely possible for one to learn how to wield these baleful energies, though at times, with great risk. With psykers generally being black sheep amongst the Imperium, for one to willfully seek out these powers often times seems like one is wishing ruination upon all of the Imperium. The rules for becoming a Sorcerer and using Sorcery are discussed in Edge of the Abyss and require GM approval.
There are some great differences between Psykers and Sorcerers that should be noted, though. First of all is how they manifest their powers. Even though they both practice to gain control of them, there is a fundamental difference. Psykers are born with the gift of psychic prowess, they are a hole in the material realm through which the Warp seeps through. With practice, they learn to hold back the ruinous energies and turn them into powers to benefit oneself and, hopefully, the Imperium. A Sorcerer, on the other hand, is not born with any innate ability with the warp, just like the normal masses. Instead, a Sorcerer actively seeks out how to rip holes in the thin lining between this realm and the Warp, hopefully for their benefit, but at a much greater risk.
Because of this, Sorcerers count as Psykers for only part of the time. When a Sorcerer manifests a power and for a number of rounds afterward equal to their Psy Rating they count as a Psyker. They exude the same essence as a psyker, Force weapons work in their hands, certain daemons are attracted to them, etc. A Sorcerer cannot suppress this energy in any way, short of moving next to a Null. A Sorcerer can emulate this effect without manifesting a power by simply making a Focus Power test, though they give off only the smallest bit of effort and do not risk complications unless something goes horribly awry. After this time, they return to being counted as a non-Psyker. The exception to this is attacks that specifically target Psykers will be half effective to a Sorcerer who hadn’t recently used a power. Also, because they don’t innately sense the Warp, the will be unaware of the presence of a Null until they try to manifest a power and it fails.
A Sorcerer in mid incantation is a frightening thing to interrupt. In most cases, simply nothing can happen, the incantation was lost. But sometimes, they lose control over their powers and can cause terrible rips and holes to form, with terrifying consequences. If, while manifesting a power at a Strength higher than Fettered, the Sorcerer is interrupted and unable to finish manifesting the power, there is a percentage chance of the power going out of hand. For each Psy Rating of the power, there is a 5% chance the power goes awry and invokes Psychic Phenomena. An incantation is interrupted if the Sorcerer must use his both his hands for something other than the incantation, like being grappled or knocked out.
Example: A Heretek Sorcerer with Psy Rating 4 has begun an incantation to summon a wreath of flame to strike against an Explorer. To make sure it’s deadly, he pushes it to increase his Psy Rating by 3. But, the Explorer was expecting this and readied an action to try and tackle the Heretek to the ground. He succeeds in his charging bull rush and knocks the Heretek to the ground. Since he was forced to stop his incantation, the power is lost, but the power might go awry. With a Psy Rating of 7 for the power, there is a total of 35% chance that the power will cause phenomena to occur, and if it does, will have all the same modifiers as if he was normally rolling on the phenomena chart.