This taint can manifest in various ways, from the subtle corruption of an individual's psyche to the wholesale adoption of alien technology and culture. The Mark of the Xenos is a reminder that, in the grim darkness of the far future, even the smallest hint of alien influence can have far-reaching consequences.
It is highly likely that refers to a specific supplement for the Deathwatch roleplaying game, published by Fantasy Flight Games (FFG) around 2011–2012.
On the ice-shrouded planet of Kalthok-IV, a remote world on the edge of Imperial space, a peculiar phenomenon had been observed. Small, seemingly insignificant markings had begun to appear on the equipment and even the bodies of the planetary defense force. These marks, an intricate pattern of lines and symbols, were the Mark of the Xenos, a sign that the planet was under the influence of a malevolent alien presence.
The sergeant called upon the expertise of Tech-Priest Elwes, an adept skilled in the mystic arts of technology and the occult. Elwes quickly deduced that the Mark of the Xenos was not a mere graffiti but a sigil of corruption, a beacon summoning an ancient, eldritch power.
| Chapter | Title | Description | | :--- | :--- | :--- | | I | | This section, the core of the book, details over 35 xenos species found in the Jericho Reach. It includes major factions like Tyranids, Tau, and Orks, as well as a host of lesser-known aliens. | | II | Radicals and Heretics | This chapter covers the "enemy within," detailing human heretics, cultists, renegade organizations, and abominations like the Magos Phayzarus, a cyborg who hunts Space Marines for their gene-seed. | | III | The Forces of Chaos | This section is dedicated to the daemonic legions of the Chaos Gods, providing stats and profiles for a range of warp-spawned horrors. | | IV | Advanced Adversaries | This chapter presents guidelines for creating truly epic and powerful threats, serving as "boss monsters" for high-level kill-teams. |
Within the Warhammer 40K universe, several Xenos factions have risen to prominence, each with their own distinct culture and agenda.