By Joseph Carriker (oakthorne@hotmail.com)
These rules were inspired by the works on diablerie in the Vampire main book, Dirty Secrets of the Black Hand as well as David S. Kaplan's Extended Rules for Diablerie.
Penalty: The force that animates the Cainite frame after mortal death is utterly tenacious. So tenacious that it is rarely destroyed -- it merely transfers hosts, latching on to the soul of the Diabolist, manifesting as black veins in the aura. Only if the victim's power is greater than his victim's (i.e. his generation is lower, thus gaining no advance in generation from the act) will the consumed soul eventually be subsumed, causing the black veins to disappear (in 40 - victim's Generation in weeks).
Penalties: The difficulty with retaining part of the victim's learning and memories is that personality, sense of self and strength of will go with it. everytime the Diabolist plumbs the stolen memories or even enters a situation that is meaningful or memorable to the victim's Animus, the Storyteller rolls Animus (dif 7). Each success subtracts one from the Diabolist's WP. Should the Animus reduce the Diabolist to 0 WP, it takes over. Note that this can happen at nearly anytime; these rolls are great for botched Hunting rolls. Imagine the Diabolist's surprise when he ends up fighting a battle just to feed on the girl who resembles the Animus' true love. While most stimuli cause one roll only, sometimes the situation is so strong the Animus is permitted additional rolls. If the Diabolist is deliberately searching his Animus' memories, the Animus is allowed one roll for every success his host scores on the recollection roll. All of this assumes the Diabolist was successful on the initial Intelligence + Empathy roll. If he fails the roll, he is simply unable to recall anything of the victim's psyche, a mixed blessing. If he should botch, however, the Diabolist loses all cohesion of the soul's thoughts and is overwhelmed by the flood of thoughts and emotions. However, he returns from this several hour (one hour per '1' rolled) catatonia with a Derangement: Alternate Personality. He gains no true Knowledges or memories (thus, no Animus rating), but periodically experiences a shift in personality wherein he believes he is his victim. Note that a Diabolist need not try to assimilate the flood of mental images, instead gritting his teeth and ignoring it. Unfortunately, many first time Diabolists try to make sense of this jumble automatically and continue to do so, unless taught otherwise. Such teaching is rare even in sects such as the Sabbat, though those on the Path of Caine or the Assamites on the Path of Blood may well be able to impart this lore.
Finally, any Derangements possessed by the victim will be gained (whether or not the Diabolist concentrates on retaining memories) unless an opposed Willpower roll between Diabolist and victim at the time of death is made. If the victim's Derangement is a temporary one (i.e. it may be bought off by spending WP), one success is sufficient to escape unscathed. If the victim's Derangement is permanent, however, a mere one success indicates that the Derangement is gained, but as a temporary one. Two or more successes is needed to overcome the Derangement in such an instance.
Second, the Diabolist gains one Discipline point per difference in Generation between himself and his victim. These points are placed in Disciplines his victim excelled in, much like is done with Knowledges. The only limitations are that they may not be added to Disciplines the victim did not have, they may not increase a Discipline if the Diabolist's rating in that Discipline is equal to or greater than the victim's, and no more than one dot may be added to a Discipline. When the victim is of higher generation, the Diabolist only gains the potential for learning his Disciplines, though the Storyteller may also allow the Diabolist to gain a single Discipline point, especially if the victim was very powerful. Though Thaumaturgy may not be learned via the forementioned potential, a dot may be placed into Thaumaturgy if the victim possesses it and the Diabolist retains the Animus of the victim. Doing so teaches the Diabolist a new ritual known by the victim as well as adding a dot in any Path known to the victim.
Penalties: The Bitter Rose has its thorns as well. First of all, the Disciplines gained are "shadow points". They must still be bought, though at half XP cost. Until this is done, the character can control the power, but there are times when it flares out of control. Thus, the vampire with Animalism may find himself suddenly surrounded by a flock of bluejays, the Potent Diabolist may accidentally break things with his newly crushing grip; the wielder of Protean may Earth Meld at the most inopportune times and the Diabolist of a Tzimisce might spontaneously shift into the dreaded zulo form at tense moments.
In addition, the weaknesses of the blood are transferred as well. Until the "shadow points" are permanently bought, the Diabolist suffers the Clan Weakness of the victim. If the two were of the same clan, the Diabolist's own Clan Weakness intensifies by a step (Gangrel lose Social Attributes with only four Frenzies, Brujah are at +3 difficulty to resist Frenzy, Tremere are an additional step toward being Blood Bound, etc.)