* AnticlimaxBoss: A relatively minor villain in ''Xenos'' is shown to be an ungodly powerful psyker. Not only could he force the submission of a Chaos Space Marine, he was able to tear a cipher for the [[spoiler: Necroteuch from the walls of the saruthi tetrascape. He ''forced a wall'' to divulge its secrets with the power of his mind. It left him largely burned out, though, too weak to stop Heldane from just shooting him.]]
** At the end of Hereticus, a Daemonhost [[spoiler:that belongs to Glaw]] was thought to be stronger than Cherubael by dint of being less stringently bound. Cherubael was apparently strong enough that he wiped the floor with it anyway, [[OffscreenMomentOfAwesome though we don't get to see it]]. He does make a note about being nastier than Eisenhorn ever imagined.
* BadassDecay: Eisenhorn himself undergoes an in-universe version as he gets older. By the end he is running on fumes and sheer will.
** VillainDecay: Pontius Glaw goes from a charmingly evil MagnificentBastard in ''Malleus'' to a whining PsychopathicManchild in ''Hereticus''. [[spoiler: He does, however, manage to wipe out most of Eisenhorne's retinue in ''Hereticus'', so he's still pretty dangerous.]]
* InformedAttribute: Eisenhorn has very little interaction with aliens despite being a member of the Ordo Xenos, and seems to have made a career of locking up heretics.
* MagnificentBastard: Pontius Glaw and Cherubael definitely count.
* MoralEventHorizon: Every Chaos worshipper has already crossed the horizon at one point. However, a few examples stand out:
** Gorgone Locke's ColdBloodedTorture of Eisenhorn
** Cherubael's threat to Eisenhorn and Bequin at the climax of ''Xenos'' firmly establishes him as someone utterly evil:
-->''I will break every bone in your body and rape that girl by your side. And break every bone in her body. Then I will drag your jiggling carcasses down to the cathedral and burn out your agony centres while I wait for the bombardment to flatten this place''
** Pontius Glaw [[spoiler: trying to kill all of Eisenhorn's old friends.]]
** Inquisitor Osma's attack on ''Essene''.