Diablerie

In Vampire: The Masquerade, there's a thing called diablerie, which is essentially vampire cannibalism. Vampires can feed on each other just as well as they can mortals and animals, but feeding on another vampire allows the predator to consume the victim's soul and power as well as his vitae. If the victim is of an elder generation, then the predator can absorb that power, growing closer to Caine in the process (mechanically decreasing his Generation attribute, since being closer to one is better).

Because of the ramifications of such a shortcut to power, but also because literally any kind of upward social mobility is utter anathema to their cozy little pyramid scheme, the elders of the Camarilla rank diablerie as one of the most heinous crimes in Kindred society. Even though Tremere gained his Antediluvian-equivalent power by diablerizing Saulot, he was able to paint Saulot as a diabolist, trafficking with the powers of Hell, who needed to be destroyed and managed to wrangle himself out of annihilation.

Since anyone who commits diablerie has his crime readily visible in his aura, it is nearly impossible to hide the evidence of the act and having a black-streaked aura is sufficient evidence for a Prince to command a blood hunt against the diablerist. The proscriptions against diablerie mean that Princes tend to honor a writ of destruction called against a diablerist in another jurisdiction.

Being composed of vampiric anarchists, iconoclasts, and psychopaths, the Sabbat views diablerie as just another path to power. The early Sabbat destroyed the Lasombra Antediluvian through diablerie in 1413 and credited Gratiano de Veronese with the kill, though nobody can produce evidence of who actually consumed his/its soul; even if a group feeds communally, only one gets the juicy soul goodness of diablerie. The Assamite clan performs diablerie so often that they have the black aura permanently on them, which all other clans tend to view as a source for suspicion.

Due to the changes in mechanics for Vampire: The Requiem, diablerie isn't really worth doing anymore, as the punishment for doing so remained unchanged, the rewards have greatly diminished (essentially free XP vs. a decrease in generation that was almost impossible to get any other way), and the odds of getting caught have greatly increased.

Diablerie is also the subtitle for the official D20 TRPG adaptation of Diablo II that Wizards of the Coast released under their 3e ruleset.